Bar soap
Soap made by combining fats or oils with an alkali. A bar can be made by several processes; the recipe and the way it is handled affect the finished bar.
Soapmaking guide
Soapmaking, in plain language.
Look up common soapmaking words, from SAP values and trace to cure time and sodium hydroxide safety.
84 definitions
Basics & methods
10Saponification
The chemical reaction in which oils or fats react with an alkali to make soap and glycerin. A correctly measured recipe accounts for the type and weight of every fat.
Cold process
A method where oils and sodium hydroxide (NaOH) solution are mixed, poured into a mold, and left to finish reacting and cure. Soapmakers commonly call the NaOH solution lye solution. The mixture can warm up naturally even though it is called “cold.”
Hot process
A method where the soap batter is heated while it cooks through saponification. It can be unmolded sooner than cold-process soap, but it still needs time to dry and become a good bar.
Melt-and-pour
A ready-made soap base is melted, customized, and poured into a mold. The maker does not handle raw sodium hydroxide (NaOH) to make the base, but should still follow the base maker’s instructions.
Rebatch
Grating or chopping already-made soap, warming it until soft, then pressing or molding it again. Rebatching can change texture and appearance; it does not correct an unknown or unsafe formula.
Lye
A common soapmaking name for a strong alkali. This calculator uses sodium hydroxide (NaOH), often called lye; some soft or liquid soaps use potassium hydroxide (KOH), which is different and not interchangeable. Dry NaOH and freshly mixed NaOH solution can cause severe burns.
Sodium hydroxide (NaOH)
The alkali used by this calculator to estimate solid-bar soap formulas. Soapmakers sometimes call it lye; the calculator labels its amounts as NaOH for precision. Use the amount calculated for the exact fats in the recipe.
Potassium hydroxide (KOH)
An alkali commonly used for soft or liquid soap. Its SAP values are different from NaOH values, so do not substitute one for the other gram-for-gram.
Lye solution
NaOH dissolved in the recipe’s liquid, usually water; “lye solution” is the common soapmaking term. Mixing releases heat and fumes; use the recipe’s exact weights and follow sodium-hydroxide handling precautions.
Formula & alkali
13SAP value
“Saponification value”: the amount of alkali needed to react with a given weight of a fat or oil. Soap calculators use SAP values to estimate the required NaOH amount for a blend.
NaOH SAP
The sodium-hydroxide SAP value for a specific fat or oil. It is often written as grams of NaOH per gram of oil; a source may use a different unit, so check how its value is reported.
KOH SAP
The potassium-hydroxide SAP value for a specific fat or oil. It is generally larger numerically than the NaOH value for the same fat; the two values are not interchangeable.
Soap calculator
A tool that estimates the alkali and liquid for a recipe using the oil weights, oil-specific SAP values, and any NaOH reduction. Check its units and assumptions before weighing ingredients.
Superfat
A recipe setting that reduces the calculated NaOH from the theoretical amount needed to react with all the oils. It is a formulation choice, not a guarantee that a precise amount of a particular oil will remain free in the finished soap.
Lye discount
The percentage by which NaOH is reduced from the full theoretical amount. It is closely related to superfat in many calculators, though the terms can be used differently.
NaOH solution concentration
The percentage of a NaOH solution that is alkali by weight: NaOH divided by NaOH plus liquid. A higher concentration means less liquid in the solution; it does not change the oil SAP values.
Liquid-to-NaOH ratio
The weight of recipe liquid divided by the weight of NaOH. This ratio describes a solution alongside NaOH solution concentration; check which measure a recipe or calculator reports.
Oil weight
The combined weight of the oils and fats in a recipe, before NaOH solution or fragrance is added. Do not confuse it with total batch weight.
Batch size
The total amount of ingredients in one soapmaking run. Some recipes state batch size as oil weight; others mean all ingredients, so confirm the basis before scaling.
Oil percentage
Each oil’s share of the total oil weight. The oil percentages in a formula should add up to 100%, even when the batch is scaled larger or smaller.
Masterbatch
A larger, accurately weighed NaOH solution prepared ahead of time and portioned into multiple batches. It requires clear labeling, compatible recipes, and careful tracking of both NaOH and liquid amounts.
Water discount
Using less liquid in a recipe than a chosen reference amount. Less liquid may shorten the time to unmold, but can make the batter thicken faster; it does not mean reducing the NaOH amount.
Mixing & stages
11Emulsion
The point where the oils and NaOH solution are mixed evenly enough to stay together rather than separating. A stable emulsion is needed before the soap is poured or shaped.
Trace
A thickening stage in soap batter caused by mixing and the start of saponification. A trail left on the surface is one visual clue; appearance alone does not prove the recipe is fully reacted.
Light trace
An early, thin trace where batter is still fluid and a brief line disappears quickly. It is useful when a design needs time, but make sure the oils and NaOH solution are emulsified.
Medium trace
A thicker trace where a trail stays visible briefly before sinking in. “Medium” is a visual description, not a standardized measurement.
Thick trace
A heavy batter that holds ridges or shape. It can be difficult to pour into detailed molds, and may happen quickly with some fats, fragrances, or mixing conditions.
False trace
A look-alike thickening that happens when solid fats cool and begin to harden before the batter is truly emulsified. The mixture may separate later if mistaken for real trace.
Acceleration
When batter thickens faster than expected after an ingredient is added or the mixture is blended. Some fragrances and formula choices can shorten the time available for pouring.
Seizing
A very rapid thickening that can make soap batter stiff or crumbly before it is poured. It is different from gradual, workable trace.
Gel phase
A temporary warm stage during saponification when soap in the mold can look translucent or jelly-like. Soap can be made with or without a full gel phase.
Partial gel
When only part of a loaf warms enough to gel. It can leave a visible color or texture difference between the center and edges; it is usually cosmetic.
CPOP
“Cold process oven process”: using retained oven warmth to encourage gel phase in cold-process soap. Follow a reliable method for the mold and oven; excessive heat can cause problems.
Oils & fatty acids
14Hard oils and fats
Oils or fats that are solid or firm at typical room temperature, such as many butters and animal fats. Their properties vary; the name alone does not predict the finished bar.
Soft oils
Oils that are liquid at typical room temperature. Their fatty-acid makeup and SAP values differ, so use values for the specific oil and processing type.
Fatty-acid profile
The mix of fatty acids in an oil or fat. It helps explain how an ingredient can influence soap qualities, but does not replace its own SAP value or a tested formula.
Lauric acid
A saturated fatty acid found in some soapmaking fats. In soap, it is generally associated with strong cleansing and quick, bubbly lather; high amounts may feel drying to some people.
Myristic acid
A saturated fatty acid that can contribute to hardness, cleansing, and quick lather in soap. The result depends on the entire oil blend.
Palmitic acid
A saturated fatty acid that can contribute to a firm bar and stable, creamy lather.
Stearic acid
A saturated fatty acid that can contribute to a firm bar and dense lather. Batter rich in stearic acid can thicken quickly as it cools.
Oleic acid
A monounsaturated fatty acid found in many liquid oils. In soap it is often associated with a mild feel and a slower-developing lather; curing and the full formula matter.
Linoleic acid
A polyunsaturated fatty acid found in many plant oils. It contributes to the character of an oil blend, but large amounts of highly unsaturated oils can make a bar more prone to rancidity.
Linolenic acid
A highly unsaturated fatty acid found in some plant oils. It can contribute to a softer-feeling bar and may increase oxidation risk when present in larger amounts.
Ricinoleic acid
A fatty acid characteristic of castor oil. In soap recipes, castor oil is often used in modest amounts to support lather.
Tallow
Rendered animal fat used in some soap recipes. Its properties and SAP can depend on the animal and how the fat was prepared; use a matching source value.
Lard
Rendered pork fat used in some soap recipes. Use an SAP value that matches the ingredient and source rather than assuming all animal fats are interchangeable.
Butters in soap
Plant fats sold as butters, such as shea or cocoa butter. Check that the product is a clearly identified, unblended fat before using a published SAP value.
Bar qualities
8Lather
The foam produced when soap is mixed with water and rubbed. Lather depends on the oil blend, water, use, and bar age; more foam does not automatically mean better cleansing.
Bubbly lather
Lather with larger, quicker-forming bubbles. Some fatty acids can support it, but the blend and conditions of use also matter.
Creamy lather
Dense, fine-textured foam. Some fats can support a creamier lather, especially when balanced with oils that help create bubbles.
Cleansing
A soap-formulation term often used for how readily a bar removes oils and soil. It is not a clinical skin-care rating, and stronger cleansing is not always preferable.
Conditioning
A traditional soap-calculator label for a recipe’s predicted mild or skin feel. It is an estimate, not a regulated measurement or a guarantee for every person.
Hardness
How firm a soap bar becomes. Oil blend, water, cure time, and storage can all affect firmness; a calculator’s hardness score is only a recipe estimate.
Longevity
How long a bar lasts in use. A harder, well-cured bar kept out of standing water often lasts longer, but use and storage make a difference.
Solubility
How readily soap dissolves in water. A very soluble bar may produce lather quickly but can wear away faster if it stays wet between uses.
Additives & scent
13Essential oil
A concentrated aromatic material obtained from plants. “Natural” does not mean harmless: each essential oil has its own safe-use limits and may need an exact supplier document.
Fragrance oil
A scent ingredient or blend made for products such as soap. Use the maximum rate for the exact fragrance and soap application, not a rate copied from a different scent.
IFRA standard and use limit
Industry standards and product-category limits published by the International Fragrance Association. For soap, check the current statement for the exact fragrance and rinse-off soap category; it is a use limit, not proof that a finished formula is safe.
Colorant
A material used to color soap. Choose colorants intended for the product and follow the seller’s dosage and usage instructions; a colorant suitable for crafts may not be suitable for skin-contact products.
Mica
A shimmery mineral-based powder often used as a colorant. Some micas can change color or lose brightness in soap’s high-pH environment; check that the grade is intended for the use.
Iron oxide pigment
A mineral pigment used to color soap. Only use a grade intended for cosmetic or soap use and follow its supplier’s directions.
Clay
A fine mineral powder sometimes added to soap for color or feel. Disperse it as directed to help prevent clumps, and use a product intended for the purpose.
Chelator
An ingredient that binds certain metal ions in water. In soap it can help reduce mineral-related soap scum or discoloration; it does not replace accurate NaOH calculations.
Sodium lactate
A salt sometimes added to the NaOH solution to help unmold a bar sooner or make it feel firmer. Use the supplier’s recommended amount; it does not replace curing.
Sugar in soap
Sugar can encourage more bubbles in some recipes. It can also make batter heat up more, so measure carefully and manage temperature.
Salt in soap
Sodium chloride can change a bar’s firmness and lather depending on when and how much is added. Too much may reduce lather; salt bars use a distinct recipe approach.
Milk soap
Soap made with milk as some or all of the recipe liquid. Sugars in milk can heat and darken when mixed with NaOH, so use a tested method for that particular milk and process.
Glycerin
A substance naturally produced during saponification. It remains in properly made handmade soap and helps give the bar its characteristic feel.
Curing & troubleshooting
10Cure
The weeks after soap is unmolded when excess water evaporates and the bar’s structure continues to develop. A longer cure often makes a bar firmer and longer-lasting; it does not fix a formula with excess unreacted NaOH or an unknown recipe.
Evaporation
Water leaving the soap as it cures. This loss of moisture helps the bar firm up and last longer in use.
Soda ash
A pale, powdery surface layer, usually sodium carbonate, that can form when fresh soap reacts with carbon dioxide in air. It is usually cosmetic and is not the same as unreacted NaOH.
DOS (dreaded orange spots)
Orange or brown spots that can signal oxidized or rancid oils in soap. Causes may include old oils, storage, formula, or trace metals; a spotty bar should not be assumed to be fine based on appearance alone.
Rancidity
Oxidation or breakdown of fats that can cause an off smell or spots in soap. Fresh ingredients, suitable storage, and a balanced formula can help reduce the risk.
Glycerin rivers
Translucent streaks or veins that sometimes appear in soap as it heats and cools. They are generally a visual effect, not literal rivers of extra glycerin.
Stearic spots
Opaque specks or streaks that can form when high-melting fats cool unevenly or a batter thickens before it is fully mixed. They can be mistaken for other defects, so review the full process.
Separation
When oil or liquid visibly separates from soap batter or a finished bar. Do not assume separated soap is safe to use; have the exact recipe and process reviewed.
pH
A measure of how acidic or alkaline a water-based solution is. Soap is naturally alkaline; one pH reading or strip cannot by itself prove that a bar is correctly formulated or safe.
pH strip testing
A rough check of acidity or alkalinity using indicator paper. Results depend on the test method and the strip; a pH reading alone does not detect every formulation problem or certify soap as safe.
Safety
5PPE (personal protective equipment)
Protective gear used to reduce exposure to sodium hydroxide and splashes, such as chemical-resistant gloves, eye protection, long sleeves, and closed shoes. Follow the safety instructions for the specific NaOH product and process.
SDS (Safety Data Sheet)
A supplier document describing a chemical’s hazards, handling, storage, first aid, and other safety information. Read the SDS for the exact sodium hydroxide product before using it.
Add NaOH to liquid
Slowly add sodium hydroxide (NaOH, commonly called lye) into the measured liquid while stirring; never pour liquid onto a pile of NaOH. The mixture gets hot and can release irritating fumes; use appropriate PPE and ventilation.
Chemical burn
Damage to skin or eyes caused by a corrosive material such as sodium hydroxide (NaOH). Follow the product supplier’s first-aid instructions and seek urgent medical or poison-control guidance for exposure; do not try to neutralize a burn with another chemical.
“Zap test”
An old folk method that involves touching soap to the tongue to look for an electric-like sensation. Do not put soap or uncured batter in your mouth; use a reliable, safety-reviewed assessment method instead.