In short
- Trace, gel, superfat and cure are the four words every recipe assumes you know.
- Lye means sodium hydroxide (NaOH) for bars and potassium hydroxide (KOH) for liquid soap.
- A SAP value is how much lye an oil needs; a superfat is how much of the oil you leave unsaponified on purpose.
- Each term links to the guide that explains it properly.
Terms are in alphabetical order. Where a word has a longer story, the link goes to the guide that tells it.
A
Acceleration. Batter thickening much faster than usual, so there is less time to pour and swirl. Fragrances are the usual cause, followed by heat and a high share of hard oils. See seizing, ricing and acceleration.
Antioxidant. An additive that slows the oxidation of oils, such as rosemary extract or mixed tocopherols (vitamin E). It is not a preservative: it does nothing against microbes. See antioxidants and chelators.
Ash. See soda ash.
B
Bastile. A soap that is mostly olive oil, with some coconut or castor for lather. There is no fixed line; many makers draw it at 70 % olive oil or more. See castile soap.
Batter. The mixture of oils and lye solution once it has been blended, before it sets in the mould.
C
Castile. Soap made from olive oil alone. Many liquid soaps sold as “castile” today contain other oils. See castile soap.
Cavity mould. A mould with individual bar-shaped cavities, as opposed to a loaf that is cut into bars. See soap moulds.
Chelator. An additive that binds metal ions such as iron and copper in the bar, so they cannot speed rancidity. Tetrasodium EDTA and sodium citrate are the common ones. What a bar releases in one wash is far too little to soften hard water. See antioxidants and chelators.
Cold process (CP). Soap made by mixing oils and lye solution and letting the batch’s own heat finish the reaction in the mould. See your first cold process soap.
Colourant. Anything that colours soap: oxides, ultramarines, micas, dyes, clays and plant powders. Not all survive the high pH of soap. See colouring soap.
CPOP. Cold process oven process: putting freshly poured soap in a warmed oven, turned off, so it gels. See gel phase.
Cure. The weeks after cutting when water leaves the bar and it becomes harder, longer-lasting and milder. Four to six weeks is usual; castile takes months. See curing and storing soap.
D
Discount. See lye discount.
DOS. Dreaded orange spots: orange, rancid-smelling spots where unsaturated fats in the bar have oxidised. The superfat alone does not cause them; polyunsaturated oils, traces of iron or copper, heat and light matter more. See dreaded orange spots.
Dual lye. A recipe that uses both sodium and potassium hydroxide, common in shaving and cream soaps. See NaOH, KOH and dual lye.
E
Embed. A piece of soap set into a new batch, such as cubes, curls or shapes. See embeds and tops.
Emulsion. The first stage of mixing, when the oils and lye solution stop separating. It comes before trace. See trace.
Essential oil (EO). A concentrated aromatic oil distilled or expressed from a plant. Many have a maximum level in soap under the IFRA Standards, set by what they contain; some, such as lavender, have none. See scenting soap.
Exfoliant. Something added for scrub: ground oats, poppy seeds, pumice, coffee grounds, loofah. See soap additives.
F
False trace. Batter that looks thick because solid fats are cooling and setting, not because it is saponifying. It thins again when warmed or blended on. See trace.
Fatty acid. One of the long carbon chains that make up a fat. Which fatty acids an oil carries decides how hard, cleansing and conditioning its soap is. See fatty acids and soap qualities.
Fixed oil. An oil that does not evaporate, the kind that makes soap, as opposed to an essential oil.
Flash point. The temperature at which a fragrance’s vapour can catch fire from a flame. It matters for storage and shipping; in cold process soap it matters very little.
Fragrance oil (FO). A perfume blended for soap, from synthetic and natural materials. Suppliers give a usage rate and an IFRA certificate. See scenting soap.
Full-boiled soap. Industrial kettle soap: boiled with excess lye, then salted out so the glycerin drains away. See how soap is made.
G
Gel phase. When a loaf’s own heat turns it translucent and darker from the centre outward. It is mostly cosmetic: gel brightens colours, but gelled and ungelled soap are equally safe and, once cured, equally hard. See gel phase.
Glycerin (glycerol). The by-product of saponification. It stays in handmade soap and draws moisture from the air.
Glycerin rivers. Translucent veins through a bar. They form when a high-water loaf cools slowly after gel, and pigment, titanium dioxide above all, makes them show. Harmless. See glycerin rivers and cracks.
H
Hard oils. Oils and fats that are solid at room temperature: coconut, palm, butters, tallow, lard. They give a hard bar. See choosing oils.
Hot process (HP). Cooking the batter until saponification is complete before it goes into the mould. The soap is safe once it has cooled and set, and hardens over four to six weeks. See hot process soap.
Humectant. Something that draws water from the air: glycerin, honey, sugars, sodium lactate.
I
IFRA. The International Fragrance Association, whose Standards set the maximum level of each fragrance material by type of product. Soap is category 9. See scenting soap.
INCI. International Nomenclature of Cosmetic Ingredients: the standard names used on ingredient lists, such as Olea Europaea Fruit Oil for olive oil. See labelling soap.
Infusion. Oil or water in which herbs, flowers or roots have steeped to take up their colour. See herbs, flowers and infusions.
INS. A number made by subtracting an oil’s iodine value from its SAP value, used as a rough guide to a bar’s balance. See iodine value and INS.
Iodine value. How unsaturated an oil is, in grams of iodine per 100 g. Higher means a softer bar that goes rancid sooner. See iodine value and INS.
K
KOH. Potassium hydroxide, the lye for soft and liquid soap. It is usually sold about 90 % pure. See NaOH, KOH and dual lye.
L
Layering. Pouring batter in separate layers, often of different colours. See layers and pencil lines.
Lye. The alkali that turns oils into soap: sodium hydroxide for bars, potassium hydroxide for liquid soap. See handling lye safely.
Lye concentration. The lye as a percentage of the lye solution: lye ÷ (lye + water). A 33 % solution is our calculator’s default. See water and lye concentration.
Lye discount. Using less lye than the oils could take. It is the same number as the superfat, seen from the other side. See superfat and lye discount.
Lye-heavy. Soap with more lye than its oils can use, which makes it caustic. See soap pH and testing.
Lye pocket. A pocket of lye solution trapped in a bar because it was not mixed in. It is dangerous; the bar should not be used. See soap troubleshooting.
M
Master batch. Lye dissolved in advance at a known strength, often 50 %, and weighed out as a solution. See water and lye concentration.
Melt and pour (MP). Ready-made soap base that you melt, colour, scent and pour, with no lye to handle. See melt and pour soap.
Mica. A mineral powder coated with pigment, used for shimmer and colour. See colouring soap.
Morphing. A colourant changing colour in soap’s high pH, as some micas, dyes and plant colours do. See colouring soap.
N
NaOH. Sodium hydroxide, the lye for bar soap, sold as beads or flakes close to 100 % pure. See handling lye safely.
O
Oxides. Iron oxide (and chromium oxide) pigments. They are stable in soap and give strong matte colour. See colouring soap.
P
Partial gel. A darker circle in the middle of a cut bar where only the centre gelled. It is cosmetic. See gel phase.
Pencil line. A thin line of mica or charcoal dusted between two layers. See layers and pencil lines.
pH. A scale of acidity and alkalinity. Bar soap in a 1 % solution measures about pH 9 to 10, and that is not a fault. See soap pH and testing.
Phenolphthalein. An indicator that turns pink in alkaline conditions, used to look for free lye in soap. See soap pH and testing.
PPO. Per pound of oils, a US way of giving amounts: 1 oz of fragrance PPO is 1 oz for every 16 oz of oils, or 6.25 %. See scenting soap.
R
Rebatching. Grating finished soap and melting it with a little liquid to fix a mistake or add something that would not survive fresh lye. Also called hand-milling. See rebatching soap.
Rendering. Melting fat out of raw animal tissue and cleaning it, to make lard or tallow for soap. See lard and tallow.
Ricing. Small lumps like grains of rice forming in the batter, usually caused by a fragrance. See seizing, ricing and acceleration.
S
SAP value. Saponification value: the milligrams of potassium hydroxide needed to saponify one gram of an oil. Soapmakers often quote it as grams of NaOH per gram of oil. See SAP values explained.
Saponification. The reaction of a fat with lye that makes soap and glycerin. See how soap is made.
Seizing. Batter setting solid in the pot within seconds, usually from a fragrance. See seizing, ricing and acceleration.
Separation. Oil or liquid pooling out of the batter or the finished bar. It can mean a weighing error or an unfinished emulsion; test before you use it. See soft soap and separation.
Soda ash. A white, powdery film of sodium carbonate on the surface of a bar, formed when unreacted lye meets carbon dioxide in the air. Harmless and removable. See soda ash.
Sodium lactate. A salt of lactic acid added to the lye water to make a harder bar that unmoulds sooner. See soap additives.
Soft oils. Oils that are liquid at room temperature: olive, sunflower, canola, almond and the rest. They make a milder, softer bar. See choosing oils.
Soleseife. Brine soap: soap made with salt dissolved in its water. See salt bars.
Stick blender. An immersion blender, which brings batter to trace in minutes rather than the hour or more of hand stirring. See the equipment you need.
Superfat. The share of the oils left unsaponified on purpose, usually 3 to 8 % in a bar. It covers the natural variation of oils and makes a milder soap. See superfat and lye discount.
Swirl. Colours of batter moved through each other to make a pattern: in the pot, drop, hanger, spoon, Taiwan. See swirl techniques.
Syndet. A bar made from synthetic surfactants rather than soap, usually milder and closer to skin pH. See shampoo bars and our syndet calculator.
T
Tare. Setting the scale to zero with the empty container on it, so you weigh only what goes in. See the equipment you need.
Titanium dioxide. A white pigment used to make soap brighter. It needs dispersing first. See colouring soap.
Trace. The point at which the batter has thickened enough that a drizzle leaves a mark on the surface. Light, medium and thick trace suit different designs. See trace.
U
Unsaponifiables. The parts of an oil that lye cannot turn into soap, such as sterols, squalene and vitamin E. They stay in the bar. See the chemistry of saponification.
V
Volcano. Batter overheating in the mould until it cracks, bulges or erupts, usually from sugars, milk or too much insulation. See glycerin rivers, cracks and overheating.
W
Water discount. Using less water than a recipe’s default, which means a stronger lye solution. The batter traces faster and runs hotter, and the bars unmould sooner, with less soda ash and shrinkage. See water and lye concentration.
Z
Zap test. Touching a bar to the tongue to feel for the “zap” of free lye. We don’t recommend it: if the bar is lye-heavy, it puts caustic soap in your mouth. Phenolphthalein, a pH meter or titration answer the same question safely. See soap pH and testing.