The Science of Cleaning

From wood-ash lye to enzymatic detergents — the chemistry behind dirt, stains, and how to remove them

The Science of Cleaning

Cleaning is applied chemistry. Every product under the sink represents a chemical solution to a specific problem: breaking the bond between grease and cloth, dissolving the insoluble, neutralizing the reactive, or destroying the living. Understanding why cleaning agents work is the key to using them effectively — and to avoiding the common mistakes that make things worse.

Safety

Warning

Never mix bleach (sodium hypochlorite) with:

  • Ammonia → toxic chloramine gas (NH₂Cl)
  • Acids (vinegar, citric acid, HCl) → releases chlorine gas (Cl₂)
  • Other cleaning products unless labels confirm it is safe

These reactions can produce lethal concentrations in an enclosed room within minutes.

General principles: - Work in a well-ventilated area when using concentrated acids, bases, or bleach - Wear gloves for anything above pH 11 or below pH 3 - Rinse surfaces with water after using strong agents - Store cleaning chemicals in original containers, never in food containers

What Makes Things Dirty

Before choosing a cleaner, it helps to understand what type of dirt you are dealing with. Most dirt falls into a few chemical categories, each requiring a different approach.

Type Examples Bond to surface Cleaning approach
Non-polar (greasy) Cooking oil, butter, body oil, lip balm, crayons Hydrophobic Surfactant, solvent, hot alkaline water
Ionic / water-soluble Salt deposits, sweat (non-protein), some food residues Ionic/polar Water alone or mild detergent
Protein-based Blood, egg, dairy, grass, skin cells Denatured protein film Enzyme (protease), cold water, H₂O₂
Tannin-based Coffee, tea, red wine, berries, fruit juice Tannin–protein crosslinks Enzyme, oxidizing bleach
Mineral/inorganic Limescale (CaCO₃), rust (Fe₂O₃), hard water scale Ionic crystal/oxide Acid
Biological Mold, mildew, bacteria Biofilm/cell wall Biocide (bleach, H₂O₂, quaternary ammonium)
Pigment Ink, dye, tomato Conjugated chromophore Oxidizing bleach, solvent

Historical Cleaning Methods

Wood Ash and Lye — Prehistory to Present

The oldest recorded cleaning agents come from fire. Wood ash contains potassium carbonate (K₂CO₃, “potash”) and smaller amounts of calcium compounds. When soaked in water, ash produces a strongly alkaline solution — lye — capable of cleaning greasy surfaces and, crucially, of making soap.

Babylonian clay tablets from around 2800 BCE describe boiling fats with ashes. Egyptian papyri reference lye for washing. The chemistry is simple: the carbonate ion hydrolyses to give hydroxide ions.

\[\ce{K2CO3 + H2O -> 2K+ + HCO3- + OH-}\]

Colonial American housewives leached ash with rainwater in wooden barrels, testing the lye by floating an egg — it should float with roughly a coin-sized surface exposed. This skill remained essential until factory-made soap became widely available in the mid-19th century.

Urine — Ancient Rome

Roman fullers (cloth-workers) used stale urine as a fabric cleaner and fulling agent. Urine allowed to stand for several days undergoes bacterial decomposition of urea, releasing ammonia:

\[\ce{CO(NH2)2 + H2O ->[\text{bacteria}] 2NH3 + CO2}\]

Ammonia is alkaline and cuts through grease and protein stains. The Roman emperor Vespasian famously taxed urine collection, inspiring the phrase pecunia non olet (“money does not smell”). Roman cities had public urine collection vessels specifically for fullers.

Ammonia from synthetic sources (the Haber–Bosch process, 1913) is still used in cleaning products today — especially for glass, where its low residue leaves a streak-free finish.

Sand and Abrasives — Universal

The simplest cleaning mechanism: physical abrasion. Ground pumice, sand, and calcite were used to scour pots, whiten teeth, and scrub stone floors. No chemistry required — you are mechanically removing the soiled layer. The hazard is obvious: abrasives scratch.

Modern equivalents include scouring powders (calcium carbonate, silica), baking soda (mild), pumice paste, and microfibre cloths (which trap particles by van der Waals forces rather than abrasion).

Vinegar — Classical Antiquity

Dilute acetic acid (3–8% in white vinegar) has been used as a cleaner and preservative since ancient times. Its primary chemical action is dissolving calcium carbonate:

\[\ce{CaCO3 + 2 CH3COOH -> Ca(CH3COO)2 + H2O + CO2}\]

This makes it effective for limescale in kettles and around taps, and for hard-water marks on glass. The Romans used acetum (sour wine) to clean vessels and kill bacteria. It remains one of the most useful single-ingredient household cleaners.

See: Acetic Acid

Washing Soda — 18th Century Industry

Natural deposits of sodium carbonate (Na₂CO₃, soda ash, natron) were used in ancient Egypt and across the Mediterranean for washing, bleaching linen, and glass-making. The mineral was mined from dry lake beds (trona deposits).

The Leblanc process (1791) and later the Solvay process (1861) made sodium carbonate industrially cheap, placing washing soda in every Victorian laundry. At pH ~11.6, it is a powerful cleaner: it hydrolyses fats and precipitates hard-water minerals.

\[\ce{Ca^{2+} + CO3^{2-} -> CaCO3 v}\]

This precipitation of calcium carbonate actually softens water, freeing soap from being wasted on mineral ions.

See: Sodium Carbonate, Water Softening experiment

Chlorine Bleach — 1785

Claude Berthollet discovered in 1785 that chlorine dissolved in alkali would bleach textiles in minutes, replacing a process that previously required weeks of repeated sunlight exposure. Charles Tennant patented bleaching powder (calcium hypochlorite, Ca(ClO)₂) in 1799, and the textile industry was transformed.

Modern bleach is aqueous sodium hypochlorite (NaOCl, 3–8%). In water, it forms hypochlorous acid (HOCl), which oxidizes chromophores in stain molecules, breaking their color-causing conjugated double-bond structures, and penetrates bacterial cell walls:

\[\ce{NaOCl + H2O -> HOCl + NaOH}\]

See: Sodium Hydroxide

How Soap Works

Soap is the first industrial chemical product, and its mechanism underpins most modern cleaning.

Saponification

Soap is made by reacting fats or oils (triglycerides) with a strong base (NaOH or KOH). This reaction is called saponification:

\[\ce{(RCOO)3C3H5 + 3 NaOH -> 3 RCOONa + C3H5(OH)3}\]

Where R is a long hydrocarbon chain (typically C₁₂–C₁₈). The products are: - Sodium soap (RCOONa) — the cleaning agent - Glycerol (glycerine) — a moisturizer and by-product

Hard bar soap uses NaOH. Soft or liquid soap uses KOH (potassium soaps are more water-soluble).

Note

Try it yourself: Make Soap — Saponification

Micelles: Why Soap Removes Grease

Each soap molecule has two ends with opposite preferences:

  • Hydrophilic head (-COO⁻): attracted to water, polar
  • Hydrophobic tail (-CH₂-…-CH₃): repels water, attracted to oil

In water, soap molecules arrange themselves into micelles: spherical structures where tails point inward around trapped grease, and heads face the water. The micelle as a whole is water-soluble and carries the grease away when rinsed.

         water
    ↑   ↑   ↑   ↑
[head][head][head]
[tail][tail][tail]  ← trapped grease inside
[tail][tail][tail]
[head][head][head]
    ↓   ↓   ↓   ↓
         water

Soap Scum

Soap works poorly in hard water. Calcium (Ca²⁺) and magnesium (Mg²⁺) ions react with soap to form insoluble calcium/magnesium soaps — the grey-white “soap scum” on bathtubs and old plumbing:

\[\ce{2 RCOONa + Ca^{2+} -> (RCOO)2Ca v + 2 Na+}\]

This is why synthetic detergents (developed in the 1930s–40s) replaced soap for laundry: they are designed to remain soluble in hard water.

See: Hard Water experiment

Synthetic Detergents and Surfactants

Modern cleaning products use surfactants (surface-active agents) — molecules with the same amphiphilic structure as soap but engineered for specific properties.

Types of Surfactants

Type Charge Common examples Uses
Anionic Negative Sodium lauryl sulfate (SLS), LAS Dish soap, shampoo, laundry — best for dirt/grease
Cationic Positive Quaternary ammonium (quats) Fabric softener, disinfectants, antimicrobial
Nonionic None Alcohol ethoxylates, polysorbates Low-foam, delicate fabrics, industrial cleaning
Zwitterionic Both Betaines, amine oxides Gentle, personal care, baby products

Anionic surfactants dominate general cleaning. Cationic surfactants are used in disinfectants and fabric conditioners (their positive charge adsorbs to negatively charged fabric fibres). Nonionic surfactants work well in hard water and at low temperatures.

Hard Water and Builders

To help surfactants work in hard water, detergents contain builders — compounds that sequester calcium and magnesium: - Phosphates (now restricted in most countries due to eutrophication) - Zeolites (ion exchange, softens water) - Citrates (chelate Ca²⁺ and Mg²⁺) - EDTA (ethylenediaminetetraacetic acid) — extremely powerful chelator

See: Water Softening, EDTA

pH and Cleaning

One of the most important principles in cleaning is matching pH to the type of soil.

pH Agent Best for
1–3 HCl, phosphoric acid, sulfamic acid Heavy limescale, rust, mineral encrustations
3–5 Citric acid, acetic acid (vinegar), oxalic acid Limescale, hard water marks, rust stains, urine scale
6–8 Mild detergents, club soda Light soil, food residues, general surface cleaning
8–10 Baking soda, borax, most laundry detergents General cleaning, grease, mild deodorizing
10–12 Washing soda, ammonia, soap Heavy grease, protein stains, hard water deposits
12–14 Sodium hydroxide, strong drain cleaners Blocked drains (fat + hair), oven cleaning

The rule: acids dissolve mineral soils (limestone, rust, hard water scale); alkalis saponify and dissolve organic soils (grease, protein, oil). Neutral detergents cover moderate general soils.

See: Rainbow pH Indicator to observe the pH of household cleaning products.

Enzymatic Cleaners

Biological washing powders contain enzymes — protein catalysts that break specific chemical bonds at low temperatures. They are the most targeted cleaning agents available.

Enzyme Breaks down Stains treated
Protease Protein bonds (peptide bonds) Blood, egg, dairy, grass, sweat
Lipase Ester bonds in fats Cooking oils, butter, body fat
Amylase Glycosidic bonds in starch Pasta, potato, gravy, custard
Cellulase Cellulose microfibrils Fabric pilling, cotton brightening
Mannanase Galactomannans Chocolate, ice cream, ketchup (guar-containing)

Critical temperature rule: enzymes are denatured (permanently unfolded and inactivated) above ~55–60°C. Always use biological detergents at 30–40°C for best results. Hot washes destroy the enzymes before they can act.

Oxygen Bleach

Sodium percarbonate (2Na₂CO₃·3H₂O₂) — the active ingredient in powder oxygen bleaches — releases hydrogen peroxide when dissolved in warm water:

\[\ce{2Na2CO3 . 3H2O2 -> 2Na2CO3 + 3H2O2}\]

Hydrogen peroxide then acts as a gentler oxidant than chlorine bleach:

\[\ce{H2O2 -> H2O + [O]}\]

The nascent oxygen breaks the chromophore bonds in stain molecules. Unlike chlorine bleach, hydrogen peroxide is colour-safe, safe for most fabrics including wool, and decomposes to water — no toxic residues.

See: Hydrogen Peroxide

Chelation

Chelating agents are molecules with multiple binding sites that can “grab” metal ions and hold them in solution, preventing them from forming insoluble deposits or interfering with detergents.

EDTA forms six bonds with a single metal ion, making a cage-like complex too stable to let go:

\[\ce{Ca^{2+} + EDTA^{4-} -> [Ca-EDTA]^{2-}}\]

This is why EDTA is used in industrial descalers, pharmaceutical preservatives, and formerly in detergent builders. Citric acid performs a gentler version of the same job and is biodegradable.

See: EDTA, Hard Water

The Vinegar + Baking Soda Myth

The combination of vinegar and baking soda is one of the most widely promoted DIY cleaning recipes. The dramatic fizzing is appealing — but chemically, these two substances neutralize each other:

\[\ce{CH3COOH + NaHCO3 -> CH3COONa + H2O + CO2}\]

The product is sodium acetate — a mild salt with negligible cleaning power — plus water and CO₂ gas. The mixture ends up slightly acidic (because acetic acid is weaker and the equilibrium favours it), but far less effective than either agent used alone.

Use them separately: - Vinegar (alone) for mineral deposits and limescale - Baking soda (alone) as a mild abrasive or deodorizer

The physical action of CO₂ bubbles can help dislodge loose blockages in drains, which may be why the myth persists.

Baking Soda + Hydrogen Peroxide — A Combination That Works

Unlike the vinegar + baking soda pairing, mixing baking soda and hydrogen peroxide is genuinely useful. The two are chemically compatible and each reinforces what the other does:

  • Baking soda (pH ~8.3) raises the local pH slightly and provides gentle abrasion
  • Hydrogen peroxide is a more effective oxidant at alkaline pH

The key chemistry: at neutral-to-alkaline pH, H₂O₂ preferentially dissociates to the hydroperoxide anion (HOO⁻), which is a more reactive bleaching species than undissociated H₂O₂:

\[\ce{H2O2 <=> HOO^- + H+} \quad pK_a = 11.6\]

Baking soda shifts the equilibrium just enough to enhance oxidation without decomposing the peroxide too quickly. This is the same principle behind commercial sodium percarbonate (oxygen bleach powder) — which is essentially a stable solid form of the same combination (H₂O₂ held in a sodium carbonate matrix).

As a paste: mix baking soda with a small amount of 3% hydrogen peroxide to form a thick paste. The paste stays in contact with a surface longer than liquid alone, and the abrasive baking soda removes loosened material mechanically.

Application Method
Grout whitening Work paste into grout with a brush; leave 10 min; scrub and rinse
Underarm and sweat stains Apply paste to fabric; leave 30–60 min; wash normally
Toilet bowl Sprinkle baking soda, add splash of H₂O₂; scrub after 5 min
Yellowed whites Soak in dilute H₂O₂ (50 mL 3% per litre) with a spoon of baking soda; 30 min warm
Surface mold on grout or caulk Same as grout — paste application, leave longer

Shelf life: the paste does not keep well — hydrogen peroxide decomposes faster in alkaline conditions. Make it fresh each time.

DIY Cleaning Agents That Actually Work

Agent What to use it for
White vinegar (5% acetic acid) Kettle descaling, limescale on taps, glass cleaning, fabric conditioner replacement
Citric acid (5–10% solution) Descaling, dishwasher cleaning, rust stains, stain pre-treatment
Washing soda Greasy pots, laundry booster, drain pre-treatment
Baking soda Mild abrasive scrub, fridge deodorizer, absorbs spilled acids
Hydrogen peroxide (3%) Stain removal on white fabrics, mold, disinfection
Baking soda + H₂O₂ paste Grout, sweat stains, surface mold, yellowed whites
Borax Laundry booster, mold prevention, general multipurpose
Salt + lemon juice Copper and brass tarnish, mild rust on cast iron
Ammonia (dilute, 5–10%) Glass and windows, heavy grease — never mix with bleach

Experiments

Three experiments let you see the underlying chemistry directly.

Note

Make Soap — Saponification React vegetable oil with sodium hydroxide to produce real soap and glycerol. Observe the exothermic reaction, trace, and set. Tests the finished soap on grease.

Note

Limescale Removal — Acids vs. Minerals Compare how different acids (vinegar, citric acid, water) dissolve calcium carbonate. Measure CO₂ production and rate of dissolution. Understand descaling products.

Note

Stain Removal Testing Make test stains on fabric and systematically compare cold water, hot water, biological detergent, non-biological detergent, and hydrogen peroxide. Observe the effect of temperature on enzyme action.

Also see: - Citric Acid Volcano — acid–carbonate reaction (the same reaction behind kettle descalers) - Hard Water — detecting and measuring hardness - Water Softening — removing calcium ions - Milk of Magnesia Rainbow — pH indicator demonstration

Index 1 — By Stain Type

Use this index to find the right cleaning approach for a specific stain.

Blood

Chemistry: Haemoglobin protein, denatures and polymerises on heating.

Rules: Cold water first, always. Hot water permanently sets blood stains.

  1. Rinse in cold water immediately
  2. Apply biological detergent (protease) and leave 30 min at room temperature
  3. Wash at 30–40°C (enzyme wash)
  4. For white fabrics: hydrogen peroxide (3%) after enzymatic treatment
  5. Dried/set stains: soak in cold saltwater, then enzyme detergent

Avoid: Hot water, bleach (will set the stain permanently on most fabrics)

Coffee and Tea

Chemistry: Tannin–caffeine–protein complexes. Tannins form bonds with protein in fabric fibres.

  1. Blot immediately (do not rub — spreads tannin further)
  2. Cold water rinse
  3. Biological detergent (amylase + protease) wash at 30–40°C
  4. Dried stains: oxygen bleach soak (30 min, warm water)
  5. White fabrics: dilute hydrogen peroxide soak

Avoid: Hot water before treatment

Red Wine

Chemistry: Anthocyanin pigments (same family as red cabbage indicator, see Rainbow pH), tannins, sugars.

  1. Absorb immediately with cloth or salt
  2. Pour boiling water through the stain from height (for tablecloths — stretches fabric and flushes)
  3. Biological detergent
  4. Set stain: oxygen bleach, or white wine/soda water (dilution + mild fizzing)

Avoid: Rubbing the fresh stain

Cooking Grease and Oil

Chemistry: Triglycerides and free fatty acids — non-polar, insoluble in water.

  1. Blot excess with paper towel
  2. Dish soap (anionic surfactant) — apply neat and work in
  3. Hot water wash with detergent
  4. Heavy grease: washing soda pre-soak (alkaline hydrolysis of fats)
  5. Dried grease: ammonia solution (5%) or degreaser

Limescale and Hard Water Marks

Chemistry: Calcium carbonate (CaCO₃) and magnesium hydroxide from evaporated hard water.

  1. White vinegar: soak, spray, or wrap with vinegar-soaked cloth and leave 1–2 hours
  2. Citric acid solution (10%): faster and more effective than vinegar for heavy scale
  3. Commercial descaler (formic acid, phosphoric acid, sulfamic acid): for severe deposits
  4. Hydrochloric acid (dilute): for very heavy encrustation (use with caution)

Prevent: Dry taps and surfaces after use; water softener; EDTA-containing rinse aids

See: Limescale Removal experiment, Hard Water

Rust

Chemistry: Iron(III) oxide-hydroxide (Fe₂O₃·nH₂O) — insoluble in water, dissolves in acid.

  1. Citric acid paste or solution: effective on fabric rust stains and surface rust
  2. Oxalic acid (wood bleach, rust removers): for tough surface rust
  3. Phosphoric acid (Coca-Cola contains ~0.06%): converts rust to stable iron phosphate
  4. Dilute hydrochloric acid: for metal surfaces (rinse thoroughly and dry immediately)
  5. Mechanical removal + acid combination for heavy deposits

Prevent: Keep metal dry; oil or wax protective coatings

Mold and Mildew

Chemistry: Fungal hyphae plus mycotoxins and pigments. Requires killing spores and removing staining.

  1. Sodium hypochlorite bleach (0.5–1% solution): kills mold spores and removes colour in one step
  2. Hydrogen peroxide (3–10%): effective, safer for coloured surfaces
  3. Borax solution: fungistatic (prevents regrowth), does not kill spores as reliably
  4. White vinegar: mild antifungal, good for prevention
  5. Address ventilation and moisture to prevent return

Grass Stains

Chemistry: Chlorophyll (waxy pigment) plus proteins from cell material.

  1. Cold water rinse immediately
  2. Biological detergent (protease) at 30–40°C
  3. Pre-treat with isopropyl alcohol (dissolves chlorophyll’s waxy structure)
  4. Oxygen bleach for residual green

Avoid: Hot water before treatment

Ink (Ballpoint)

Chemistry: Oil-based ink with dye dissolved in a viscous glycol solvent.

  1. Isopropyl alcohol (most effective — dissolves the glycol vehicle)
  2. Hairspray (alcohols and acetone in many formulations — older method that still works)
  3. Dish soap after alcohol treatment to remove residue
  4. Fresh stains respond better; old stains may have partially polymerized

Urine (on fabric or tile)

Chemistry: Urea, uric acid crystals (after drying), ammonia from bacterial decomposition.

  1. Blot immediately; do not rub
  2. Cold water rinse
  3. Enzymatic cleaner (urease + protease) — essential for uric acid crystal removal
  4. Biological detergent wash
  5. For odour after cleaning: baking soda paste, leave to dry, vacuum

Avoid: Ammonia-based cleaners (add to the smell without removing uric acid), steam (sets proteins)

Sweat and Deodorant Stains

Chemistry: Sweat contains proteins, salts, and fatty acids. The yellow staining on white fabric armholes is not sweat itself but a reaction product of aluminium salts in antiperspirant with sweat proteins — an aluminium–protein complex that is both yellow and difficult to remove.

  1. Baking soda + hydrogen peroxide paste: most effective — the peroxide oxidises the chromophore in the aluminium–protein complex, baking soda provides mild abrasion and alkaline pH boost. Apply paste, leave 30–60 min, then wash.
  2. White vinegar pre-soak: the acidity can break aluminium–protein crosslinks; soak 30 min before washing
  3. Biological detergent (protease): for the protein component
  4. Aspirin (acetylsalicylic acid) dissolved in warm water: an old remedy that works by acid hydrolysis of the crosslinks

Avoid: Hot wash before treating (sets the protein); bleach on the aluminium component (can worsen discolouration)

Candle Wax

Chemistry: Long-chain hydrocarbons (alkanes, esters) — non-polar, melt at 50–70°C.

  1. Freeze: apply ice to harden wax, chip off the majority
  2. Melt and blot: iron over paper towels to absorb wax
  3. Isopropyl alcohol or white spirit on residue
  4. Wash with detergent

Tarnished Silver and Copper

Chemistry: Silver sulfide (Ag₂S, black) and copper oxide/sulfide patina.

  1. Silver: aluminium foil + baking soda + hot water (electrochemical reduction — see Copper Reduction)
  2. Copper: salt + lemon juice or vinegar (acid dissolves oxide; chloride ions aid cleaning)
  3. Commercial silver polish (mild abrasive + reducing agent)

Glass Surfaces

Chemistry: The challenges depend on the type of soil. Mineral deposits are the most common problem; the main risk with glass is leaving residue (streaks) that is as visible as the original soil.

Hard water marks and mineral haze:

  1. White vinegar (undiluted or 50/50 with water): dissolves calcium carbonate — spray, leave 5 min, wipe
  2. Citric acid solution (5%): faster, no smell, better for heavy deposit
  3. Newspaper: slightly abrasive texture and mild acids in the ink; an old technique that works well on windows

Fingerprints and grease:

  1. Dish soap in warm water, then polish dry — do not leave water to dry on glass
  2. Ammonia solution (5–10%): evaporates cleanly with no residue; excellent streak-free result on windows
  3. Isopropyl alcohol (70%): evaporates quickly, no residue

General principle for streak-free glass: streak marks are almost always dried mineral residue from the rinse water, or soap film that was not fully removed. Use deionised water for the final wipe, or wipe with a dry microfibre cloth immediately after cleaning.

Avoid: Abrasive powders or scourers on glass (permanent scratching); neat bleach (can etch some glass coatings).

Burnt-on Food (Ovens, Pans, Baking Trays)

Chemistry: Burnt food is pyrolysed organic matter — fats and proteins that have been exposed to high heat and undergone carbonisation and polymerisation. The result is a hard, cross-linked carbonaceous crust that is essentially insoluble in water and resistant to mild surfactants.

Oven interior:

  1. Sodium hydroxide (commercial oven cleaner, ~5–10% NaOH): the most effective approach — strong alkali hydrolyses remaining ester and amide bonds in the carbon matrix, and saponifies any residual fat. Apply cold, leave overnight in a sealed oven, wipe off
  2. Ammonia overnight method: place a bowl of concentrated ammonia in a cold oven overnight (sealed). The fumes penetrate and loosen deposits without applying liquid directly. Ventilate thoroughly before wiping
  3. Baking soda paste + hydrogen peroxide: gentler and safer — apply thick paste, leave several hours or overnight, scrub with a non-scratch pad. Less effective on heavy carbonised deposits but works well on moderate grease
  4. Pyrolytic cleaning (if oven has the function): heats to ~500°C and burns deposits to ash. No chemicals needed; residue can be wiped away cold

Baking trays and roasting pans:

  1. Soak in hot water + washing soda (sodium carbonate) for 1–2 hours — softens the deposit
  2. Baking soda + hydrogen peroxide paste: spread over the pan, leave 1 hour or overnight, scrub off
  3. Dishwasher tablet dissolved in boiling water in the pan: the alkaline detergent + enzyme + abrasive combination attacks the polymerised fat layer

Non-stick pans: avoid all abrasives and harsh alkalis — they damage the coating. Hot soak only; a wooden or silicone spatula to loosen deposits.

Tile and Countertop

Chemistry: The correct approach depends entirely on the surface material.

Before using any acid-based cleaner, identify the surface:

Surface Acid-safe? Notes
Ceramic or porcelain tile Yes Glazed surface resists acid well
Glass tile Yes
Natural stone: marble, travertine, limestone No CaCO₃ — acid dissolves the surface
Natural stone: granite, slate Mostly Granite is acid-resistant; some granites contain carbonate veins
Composite quartz (Silestone, Caesarstone) Yes Engineered, acid-stable resin binder
Laminate (Formica) Yes Avoid prolonged soaking
Grout (cement-based) Dilute only Grout contains calcium compounds; prolonged acid exposure degrades it

Ceramic and porcelain: 1. General cleaning: hot water + dish soap 2. Limescale and hard water haze: vinegar or citric acid solution; spray and leave before wiping 3. Grout staining (mold, grime): baking soda + hydrogen peroxide paste worked into grout with a brush; or dilute bleach solution (rinse thoroughly) 4. Heavy grout soiling: oxygen bleach paste or dilute bleach — leave 10 min, scrub

Natural stone (marble, limestone, travertine): 1. Never use vinegar, citric acid, or any acid — they etch the surface permanently 2. pH-neutral stone cleaner or plain warm water with a small amount of dish soap 3. Baking soda paste for mild staining (pH ~8.3 — safe for stone) 4. Rinse thoroughly — do not let any cleaner dry on the surface 5. Seal regularly with stone sealer to prevent stain absorption

Metal Cookware and Silverware

Different metals require very different approaches.

Stainless steel pots and pans:

  1. Burnt food: soak in hot water + dish soap; use a non-scratch scrubber. Boiling water in the pan loosens stuck residue
  2. Discolouration (rainbow heat staining — oxidation of chromium): white vinegar on a cloth, rub along the grain
  3. Limescale inside: fill with water + a tablespoon of citric acid or vinegar, boil briefly
  4. Polish: Bar Keepers Friend (oxalic acid + feldspar abrasive) removes rust stains and restores shine — always rub along the grain
  5. Avoid: chlorine bleach (chloride ions pit stainless steel), steel wool across the grain (permanent scratching)

Cast iron:

  1. Never use soap (strips the polymerised oil seasoning layer that makes cast iron non-stick)
  2. Hot water + stiff brush or chain mail scrubber while still warm
  3. Coarse salt + a cut potato or paper towel: abrasive + mild acid; effective on stuck food
  4. For rust: scrub with steel wool + citric acid or vinegar (dilute); re-season immediately after
  5. After cleaning: dry thoroughly on the hob over heat; apply a thin coat of oil while hot

Copper pots:

Copper forms a green or brown patina of copper(II) carbonate, oxide, and sulfide compounds. This is chemically interesting and sometimes desirable, but can be removed:

  1. Salt + lemon juice or vinegar: classic method. The acid dissolves the oxide/carbonate; chloride ions assist
  2. Ammonia (dilute): forms the deep blue tetraamine copper complex — dissolves patina quickly, but rinse thoroughly to prevent over-cleaning
  3. Ketchup: acetic acid + citric acid + tomato compounds; works as a mild cleaner
  4. Commercial copper polish (thiourea-based): forms a complex with copper, removing the patina chemically

See: Colors of Copper

Silverware:

Silver tarnish is silver sulfide (Ag₂S), formed by reaction with traces of hydrogen sulfide in the air. Unlike rust, Ag₂S is electrically conductive — this enables an elegant electrochemical cleaning method:

  1. Aluminium foil method (electrochemical, best for pieces): line a container with aluminium foil, add hot water and two tablespoons of baking soda or washing soda, submerge silver pieces touching the foil. The galvanic cell reduces Ag₂S back to silver:

\[\ce{3Ag2S + 2Al -> 6Ag + Al2S3}\]

The tarnish migrates electrochemically to the aluminium — no polishing needed, no silver is removed, and the smell of H₂S released is confirmation the reaction is working.

  1. Silver polish (mild abrasive + reducing agent): physically removes the Ag₂S layer but also removes a tiny amount of silver each time
  2. Toothpaste: a mild abrasive that works, but scratches — use only as a last resort
  3. Avoid: chlorine bleach (tarnishes silver further and can cause irreversible damage)

See: Silver Mirror Reaction, Copper Reduction

Knife Marks on Plates

The grey lines that appear on white ceramic or porcelain plates after cutting food are almost universally mistaken for scratches. They are not scratches — they are metal transfer marks: tiny particles of steel from the knife blade deposited onto the glazed surface.

How to tell: run a fingernail over the mark. If the surface feels smooth and flat, it is a metal deposit. A true scratch has a raised edge or a tactile groove.

This distinction matters because a metal deposit can be removed without touching the glaze. A true scratch cannot.

Why it happens: the ceramic glaze (typically alumina-silicate based) has a Mohs hardness of 6–7. A steel knife blade is around Mohs 5.5–6.5. The knife is barely hard enough to scratch glazed porcelain, but the metal readily smears under pressure. The grey particles are iron and iron oxide from the knife.

Removal:

  1. Bar Keepers Friend (powder or cream, contains oxalic acid and a mild abrasive): most effective — oxalic acid dissolves iron oxides, the abrasive lifts particles. Apply with a damp cloth, gentle circular rubbing, rinse
  2. Baking soda paste: mild abrasive, effective for light marks
  3. Citric acid paste + gentle rubbing: dissolves iron oxide particles
  4. Cream of tartar + water paste: similar mechanism to citric acid
  5. Melamine foam (magic eraser): micro-abrasive; effective on glaze

Avoid: aggressive abrasives (silicon carbide scourers) or steel wool — these genuinely do scratch the glaze.

Index 2 — By Cleaning Chemical

Use this index to understand what each chemical is good for and where to use it safely.

Acetic Acid — Vinegar (5% solution, pH ~2.4)

Mechanism: Acid dissolution of carbonates and phosphates; mild general surfactancy.

Best for Avoid on
Kettle and appliance descaling Marble, limestone, natural stone
Limescale on taps and showers Cast iron (accelerates rust)
Hard water spots on glass and mirrors Acetate fabrics
Fabric conditioner replacement (removes soap residue) Bleach (produces chlorine gas)
Mild disinfection

See: Limescale Removal experiment

Citric Acid — Solution (5–15%, pH ~2.2 at 10%)

Mechanism: Stronger acid than acetic acid; additionally chelates Ca²⁺ and Mg²⁺.

Best for Avoid on
Heavy kettle and boiler descaling Marble and natural stone
Dishwasher cleaning Prolonged contact with metals (mild corrosion)
Rust stains on fabric
Boiler and pipe descaling
Stain pre-treatment

See: Citric Acid Volcano, Limescale Removal experiment

Baking Soda — Sodium Bicarbonate (pH ~8.3)

Mechanism: Mild abrasive (Mohs ~2.5); neutralises acidic odour molecules; mild base.

Best for Avoid on
Gentle scrubbing of sinks, enamel, stainless steel Aluminium (mild etching)
Fridge and bin deodorising Very fine polished surfaces (scratches possible)
Absorbing and neutralising acid spills
Carpet freshener (dry application)
Coffee pot and thermos deodorising

Note: Does not have significant germicidal action. Use hydrogen peroxide or bleach for disinfection.

Washing Soda — Sodium Carbonate (pH ~11.6)

Mechanism: Strong base; saponifies fats; precipitates Ca²⁺/Mg²⁺ (softens water).

Best for Avoid on
Heavy greasy pans and baking trays Aluminium (reacts with NaOH produced)
Laundry booster for white cottons Delicate fabrics
Drain pre-treatment (weekly maintenance) Painted or lacquered surfaces
Stripping old paint (high concentration)
Cement and mortar cleaning

Boric Acid and Borax — Sodium Tetraborate (pH ~9.3)

Mechanism: Alkaline; bacteriostatic and fungistatic; buffering action.

Best for Avoid on
Mold prevention (laundry, bathroom) Children’s toys or surfaces children touch
Laundry booster
Multipurpose spray (dilute solution)
Toilet bowl cleaning
Ant and cockroach control (different use)

Ammonia — Solution (5–10%, pH ~11)

Mechanism: Alkaline; saponifies fats; volatile (no residue left on glass).

Best for Avoid on
Glass and windows (streak-free) Any surface that will contact bleach
Heavy grease on hobs and extractor fans Wool and silk (degrades protein fibres)
Oven cleaning (with heat, 10% solution) Copper and brass (forms complexes, may damage)
Pre-soaking heavily stained items
Warning

Never mix ammonia with bleach. The reaction produces chloramine gases (NH₂Cl, NHCl₂, NCl₃), which are toxic at very low concentrations.

Hydrogen Peroxide — (3%, pharmacy grade; pH ~6)

Mechanism: Oxidising agent; breaks conjugated chromophore bonds; disinfectant.

Best for Avoid on
Stain removal on white and coloured fabrics Delicate dyes (especially at higher concentrations)
Blood and protein stains Silk and some wools at high concentration
Mold removal (colour-safe) Metal surfaces (accelerates oxidation)
Wound disinfection
Teeth whitening products
Fruit and vegetable washing (food safety)

Decomposition: H₂O₂ breaks down to water and oxygen on contact with enzymes (catalase in blood, peroxidase in plant material). Store in a dark container — light accelerates decomposition.

Sodium Hydroxide — Lye, Caustic Soda (pH ~13)

Mechanism: Very strong base; directly saponifies fats; hydrolyses proteins and hair.

Best for Avoid on
Blocked drains (fat + hair dissolver) Aluminium, zinc, tin (react violently, produce H₂)
Oven cleaning products Glass (slight etching with prolonged contact)
Soap making (deliberate saponification) Skin (caustic burns)
Paint stripping
Warning

Wear gloves and eye protection. Sodium hydroxide causes severe chemical burns on contact with skin. Dissolving it in water is strongly exothermic — add solid NaOH to water, never the reverse.

See: Make Soap — Saponification experiment

Hydrochloric Acid — Muriatic Acid (pH 0–1 at 10%)

Mechanism: Very strong acid; dissolves virtually all mineral deposits and metal oxides.

Best for Avoid on
Severe limescale (toilets, pipes, tiles) Stainless steel (pitting corrosion)
Rust (metal surfaces, concrete) Natural stone (dissolves the stone too)
Brick and mortar cleaning Bleach (produces chlorine gas)
Swimming pool pH adjustment Skin and eyes
Warning

Ventilate thoroughly. HCl fumes are corrosive to the respiratory tract. Use only in very dilute solutions (1–5%) for domestic applications. Never mix with bleach.

EDTA — Ethylenediaminetetraacetic Acid (pH variable)

Mechanism: Chelation — forms stable complexes with Ca²⁺, Mg²⁺, Fe²⁺, Fe³⁺, and other metal ions.

Best for Avoid on
Iron (rust) staining on fabric and grout Rarely causes problems — very selective
Descaling when acid is too aggressive
Hard water scale in industrial equipment
Keeping cut flowers fresh (chelates Ca²⁺ in water)

See: Hard Water

Salt (Sodium Chloride) — NaCl

Mechanism: Coarse abrasive; osmotic effect; catalytic in acid/metal reactions.

Best for Avoid on
Combined with lemon juice for copper and brass Steel and iron (promotes rust)
Absorbing fresh wine or juice spills (osmosis draws liquid out)
Cutting board cleaning with lemon (abrasive + acid)
Preserving and drawing out stains while fresh

Alcohols — Isopropyl Alcohol and Ethanol

Alcohols are polar organic solvents — they sit between water (very polar) and hydrocarbons (non-polar), dissolving a wide range of substances that neither water nor detergent can touch. They also evaporate cleanly, leaving no residue, which makes them ideal for surfaces where water or soap film would be a problem.

The two alcohols used in cleaning:

Alcohol Common names Typical concentration Notes
Isopropanol (2-propanol) IPA, rubbing alcohol, isopropyl alcohol 70% or 99% Most widely used; lower toxicity than ethanol for skin contact
Ethanol (ethyl alcohol) Surgical spirit, methylated spirits, denatured alcohol 70–96% Methylated spirits contains ~5–10% methanol to prevent drinking; do not ingest

Why 70%, not 100%, for disinfection:

Pure alcohol evaporates too fast to fully denature proteins on a surface. Water slows evaporation, extending contact time and allowing the alcohol to penetrate cell walls and coagulate proteins more completely. 70% IPA is more effective as a disinfectant than 99% IPA, and also less aggressive on surfaces.

\[\ce{protein\ (native) ->[\text{IPA + H2O}] protein\ (denatured, aggregated)}\]

The antimicrobial mechanism operates on two levels simultaneously: protein denaturation and disruption of lipid cell membranes. This is why alcohols are effective against enveloped viruses (which have a lipid coat) as well as bacteria.

Mechanism as a cleaning solvent:

Alcohols dissolve substances through a combination of weak hydrogen bonding and van der Waals interactions. They are effective on: - Oil-based inks and dyes (the glycol carrier in ballpoint ink is miscible with IPA) - Adhesive residues (acrylic pressure-sensitive adhesives dissolve readily) - Light greases and oils (moderate, not as effective as alkaline degreasers) - Marker and pen inks

Best for Avoid on
Electronics cleaning (keyboards, circuit boards, contacts) — 99% IPA Acrylic / Perspex / polycarbonate (causes crazing — stress cracking)
Adhesive and sticker residue Lacquered or shellac-coated wood (dissolves the finish)
Ballpoint and permanent marker ink on hard surfaces Some printed or screen-printed surfaces
Glass and mirrors (streak-free; evaporates completely) Large areas without ventilation (fire risk)
Disinfecting surfaces — 70% IPA or ethanol Untreated rubber (can degrade over time)
Thermal paste removal (CPU/heatsink) — 99% IPA
Removing nail polish residue from surfaces
Degreasing before painting, gluing, or soldering
Warning

Alcohols are flammable — flash point ~12°C (IPA) and ~13°C (ethanol). Do not use near open flames, sparks, or hot surfaces. Ventilate when using on large areas. The vapour is heavier than air and can accumulate.

Methylated spirits / denatured alcohol: contains methanol (typically 5–10%) to make it poisonous and undrinkable. Suitable for the same cleaning tasks as ethanol but never for skin contact or in food-contact applications. The methanol content has no significant effect on cleaning performance.

IPA concentrations and uses:

Concentration Best use
70% Disinfection, general surface cleaning
91% Faster evaporation, light degreasing, some adhesive removal
99% Electronics (minimum water content), thermal paste, precision optical cleaning

Acetone — Propanone

Acetone (CH₃COCH₃) is a ketone — structurally similar to alcohols but without the hydroxyl group. It is the most aggressive of the common household solvents: more powerful than IPA, faster-evaporating, and capable of dissolving polymer networks that alcohols cannot touch. It is also one of the safest organic solvents toxicologically — the human body produces and metabolises it naturally during fat metabolism (ketosis).

Mechanism: Acetone is a polar aprotic solvent. It has a strong dipole from the carbonyl (C=O) group and accepts hydrogen bonds, but cannot donate them. This gives it an unusually wide solubility range — it dissolves both polar substances (many polymers, resins, lacquers) and moderately non-polar ones. It attacks polymer chains by inserting between them and breaking the non-covalent forces holding them together, which is why it dissolves so many plastics.

Key uses:

Use Notes
Nail polish removal Dissolves nitrocellulose (the film-forming polymer in most nail polish)
Super glue (cyanoacrylate) removal One of the only solvents that penetrates cured CA; soak or apply repeatedly
Adhesive and label residue More effective than IPA for stubborn residues
Degreasing metal before painting, gluing, or soldering Fast-evaporating, leaves no residue
Removing permanent marker from hard non-plastic surfaces
Paint and lacquer stripping (small areas)
Fibreglass and resin work cleanup

What acetone will damage or destroy:

Material Effect
Acrylic / Perspex / PMMA Dissolves completely — catastrophic damage
Polystyrene Dissolves
ABS plastic Softens and dissolves (this is used intentionally in 3D printing to smooth ABS surfaces)
PVC Softens and damages
Acetate and rayon fabrics Dissolves the fibre
Painted or varnished surfaces Strips the finish
Lacquered wood Dissolves the lacquer
Printed markings on PCBs and equipment Erases labels and component markings
Rubber seals Swells and degrades

Safe surfaces: glass, stainless steel, aluminium, most ceramics, polyethylene (HDPE/LDPE), polypropylene, PTFE (Teflon), cured epoxy.

Warning

Acetone is highly flammable — flash point −20°C, far below room temperature. The vapour ignites easily and is heavier than air, pooling at floor level. Never use near flames, sparks, or heated surfaces. Work outside or with strong ventilation. Do not store near heat sources.

Comparison with IPA:

Property IPA (70%) Acetone
Flash point ~12°C −20°C
Boiling point 82°C 56°C
Evaporation Moderate Very fast
Dissolves plastics? Minimal Many common types
Disinfectant? Yes No
Safe on electronics? Yes (99%) Risky (removes markings, may damage coatings)
Skin contact Drying Drying; not a sensitiser

Nail polish remover: most commercial products are diluted acetone (with water or oil) or acetone-free formulations using ethyl acetate. Pure acetone is more effective but harsher on skin and the cuticle. Acetone-free removers are gentler but require more effort.

Further Reading