Natural Soap Directory™

Glossary of Soap Terms

This glossary contains a list of terms related to soap and to the process of making soap.

Any ingredient added to soap that is not part of the soap itself is considered an additive. Therefore, any ingredient excluding lye, water, and oils/fats/butters are additives. Examples of additives are colorants, fragrance materials, and preservatives. Additives may include herbs, micas, salt, grapefruit seed extract, excess oils/fats/butters that remain unsaponified, vitamins, clays, and etc.
Batch Code
A numbered record of each batch of soap. The Batch Code Sheet lists the company of manufacture, the name of the soap maker(s), the date made, the ingredients, the ingredients' sources and amounts, the ingredients' lot numbers, any variation from the normal soap making procedure, the cure date or "do not use before" date, the expiration date, and any additional comments.
A corrosive substance that burns or destroys organic tissue by chemical action. Caustic can refer to an acid or a base but is typically used to describe the action of an alkaline base. Lye is a caustic substance.
Complaint File
A complaint file contains a record of a customer complaint, the date of the complaint, and the action taken by the soap maker.
The propensity of a material to dissolve or melt when in open contact with air. Lye has deliquescent properties.
Characterized by the release of heat, often due to a chemical reaction. Soap is made as the product of an exothermic reaction between lye and fat.
Flash Point
The lowest temperature at which the vapors of a liquid will ignite in the presence of an ignition source. Soap makers must take care when heating fixed oils and when using essential oils because both are flammable and some essential oils have low flash points; they can suddenly break into flames when heated.
Gel Phase
An early phase of the saponification process, when the soap batter temporarily becomes a warm transparent gel and slowly returns to being opaque, slightly more solid, and cooler. Not all soap batches and all soap batters go through a gel phase.
The tendency of a material to absorb moisture from air. Lye has hygroscopic properties.
Refers to either sodium hydroxide or potassium hydroxide. Sometimes refers to a solution of either sodium hydroxide or potassium hydroxide dissolved in water. Lye is used to make soap.
Lye Discount
The practice of withholding lye from a soap formula. After determining the amount of lye needed to completely saponify the fats, only a percentage of the lye is actually used. For instance, if a 5% lye discount is desired, the amount of lye is first calculated to completely saponify the oils/fats, then only 95% of the calculated amount of lye is actually used; 5% is withheld.
Lye Solution Preparation
When combining lye with water, always add the lye slowly to cool water while stirring carefully. The lye-water solution should not be splashed while stirring. Whenever lye is dissolved in water, vapors are released into the air. The vapors appear as steam or mist and contain molecules of lye. Always prepare the lye-water solution in a well-ventilated area with incoming fresh air, not re-circulated air. When dissolving larger quantities of lye (20 pounds or more), either prepare the solution outdoors, use a fan to aid in the dispersal of vapors, or wear protective respiratory equipment. The lye-water solution should be prepared in a location with access to a sink or water hose because first aid for contact with lye involves flushing the contact area with plenty of fresh water for 20 minutes. Protective eyewear, such as safety glasses or goggles, should be worn when preparing the lye-water solution because allowing even a small drop of lye-water solution to contact the eye can cause blindness. The dissolution of lye into water releases heat, which will raise the temperature of the solution. If the temperature of the lye-water solution reaches its boiling point, which is just under 212° F (100° C), the solution will boil. Use a calibrated thermometer to monitor the temperature of the solution while adding the lye. The temperature of the solution should not be allowed to exceed 190° F (90° C). The temperature of the lye-water solution can be reduced by placing the container of lye-water solution in a bath of ice water. When making large amounts of lye-water solution that are too large to place in a bath of ice water, either use cold refrigerated water or substitute ice cubes for part of the water for the solution.
Materials Not Suitable for Contact with Lye
Do not use these materials in contact with lye or lye-heavy soap: Aluminum, brass, bronze, chromium, iron, magnesium, tin, zinc, and most metals (other than stainless steel), and items made of metal and coated with Teflon. When lye reacts with these listed metals, hydrogen gas is generated which is extremely flammable and explosive. Never add sugar to lye solutions; lye may react with various sugars to generate carbon monoxide, which is a poisonous gas.
Materials Suitable for Contact with Lye
Materials that are suitable for contact with lye at room temperature are high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), silicon rubber, stainless steel, glass, and porcelain. Stainless steel is most suitable for contact at elevated temperatures. Plastics may soften at higher temperatures and a test should be first made of their suitability.
"Material Safety Data Sheet." Contains pertinent information related to the following safety categories for a specific material: Manufacturer or vendor information, chemical composition, hazards and potential health effects, first aid measures, fire fighting measures, spill measures, handling and storage, exposure and protection, physical and chemical properties, stability and reactivity, toxicological information, environmental information, disposal considerations, transportation information, and regulatory information.
Molecular Weight
The mass of one mol of molecules calculated using standard atomic weights. It is typically expressed as grams/mol (g/mol). One mol of molecules contains a definite number of molecules; 1-mol of molecule A has the same number of molecules as 1-mol of molecule B. When making soap, 3-mol of lye is needed to react with 1-mol of fat in order to achieve 100% saponification. Molecular weight is used to convert moles to mass in order to provide weights for soap recipes.
Oils: Essential Oils
Volatile oils extracted from plant matter by either distillation (steam or water), expression, or chemical solvents. Essential oils may be used to add fragrance to scented soaps.
Oils: Fixed Oils
Refers to oils that can be raised to a high temperature without evaporating. Fixed oils (such as olive oil, palm oil, and coconut oil) are commonly used to make soap.
Oils: Fragrance Oils
Also known as aroma oils and aromatic oils. These oils are blends of synthetic aromatic chemicals that may be diluted with a carrier such as propylene glycol, vegetable oil, or mineral oil. Fragrance oils may be used to add fragrance to scented soaps.
Scale to measure the acidity or alkalinity of a chemical typically dissolved in water. The measurement scale goes from 0 (very acidic) to 14 (very alkaline or very basic), with pH of 7 representing neutral. Lye, a corrosive chemical used to make natural soap, has a pH of 14. Water, also used to make soap, has a pH of 7 and cured soap should have a pH between within the range of 8 to 10.
pH Strip Test
Used to test for un-reacted lye in soap. pH strips may be purchased from most chemical supply companies, laboratory supply companies, and pool supply companies. pH strips used to test the pH of soap should include a scale from 7 to 14. To test with a pH test strip, put one gram of soap in 100-ml (100-g) of room temperature (25° F/77° C) water (having a neutral pH of 7), let the soap dissolve, and test with a pH strip by dipping it into the soapy water. Results for un-reacted lye in soap typically exceed 10 pH. Results for cured soap (no longer containing lye) may range from 8 to 10 pH. The reading of the pH test strip is dependent upon the interpretation of the soap maker and may be subject to error.
pH Tongue Test
Used as a quick informal test for un-reacted lye in soap. Touch tongue to soap bar, or rub wet finger on soap and then touch finger to tongue. If a tingling, pinching, or burning sensation is felt, then the soap contains un-reached lye and is not ready for use. This test is greatly dependent upon the interpretation and sensitivity of the soap maker.
Potassium Hydroxide
KOH; CAS Registry Number: 1310-58-3; Molecular Weight: 56.11 g/mol. Also referred to as caustic potash, potash, potash lye, and potassium hydrate. It is a corrosive chemical that has a pH of 14, indicating it is a strong base. Potassium hydroxide is used in soap making to react with oils and fats to produce soap, frequently liquid soap.
Safety Equipment
Safety equipment for making soap includes eye protection, a face shield, rubber gloves, and clothing to cover any bare skin that may be exposed to lye, including arms, legs, and feet. Ventilation equipment may be required when making large quantities of lye-water solution. Further safety equipment should include a smoke alarm, fire extinguisher, easy access to a telephone, a first aid kit, and easy access to fresh running water, such as from a sink or hose.
Saponification Process
Saponification Process
This annimated diagram of the saponification process repeats in an indefinite loop.
"Saponification" refers to the chemical reaction between fat and lye that results in the formation of glycerin and soap.
Saponification occurs when, first, three molecules of sodium hydroxide (NaOH) are dissolved in water (H2O) and are split apart, which results in three sodium ions (Na) and three hydroxyl groups (OH). Second, a triglyceride (fat) molecule (C3H5(COOR)3) is split apart through hydrolysis, which results in a free glycerol (C3H5) and three fatty acid tails (COOR). Third, the hydroxyl groups (OH) all bond to the free glycerol (C3H5) to form a molecule of glycerin (C3H5OH3). Forth, the three fatty acids (COOR) each bond with one of the three sodium ions (Na) to form three molecules of soap (3NaCOOR).
When the precise ingredients have completed the saponification process, one molecule of glycerin will be present for each three molecules of soap; no molecules of lye (sodium hydroxide) remain in the soap; they have all been split apart and used to form the soap molecules and glycerin.

To create a link to the saponification process diagram, please use the following permanent address.

SAP Value
"Saponification Value." The number of milligrams of lye required to completely saponify one gram of a specific fat. While soap makers commonly refer to the sap value as the measured amount of sodium hydroxide, laboratories commonly refer to the amount of potassium hydroxide; either is correct, so specification is required. Commonly, oil distributors use the number of milligrams of potassium hydroxide because the sap number is provided by the processor's test lab. Saponification charts found on the Internet as aids for formulating soap recipes commonly use the number of milligrams of sodium hydroxide. Therefore, it is very important to be certain if a given sap value refers to sodium hydroxide (NaOH) or potassium hydroxide (KOH).
Condition of soap batter when the ease of mixing and pouring is arrested. A phase of cold process and hot process soap making when the soap batter becomes too thick to pour into a mold. Seizing occurs when saponification has progressed to the point that the soap batter is no longer liquid and has begun to solidify.
Soap Making Process: Cold Process
Cold process (CP) soap making is the process where lye is dissolved in water to form a solution. The lye-water solution is then added to melted fats and oils and constantly stirred or mixed with a hand blender. After trace is detected, scents, herbs, and/or colorants may be added to the soap batter. After trace but before seize, the cold process soap batter is poured into molds. The molds are usually insulated with blankets or towels. Within 24 hours, the soap batter hardens sufficiently to be removed from the mold and to be sliced into bars. Fresh bars of cold process soap must cure on drying racks for four to six weeks to allow the lye to completely saponify the fats and oils into soap. After four to six weeks of cure, cold process soap should be ready for use and should not contain any lye. This process is referred to as "cold" process soap making because no heat from an external source is added to the soap batter.
Soap Making Process: Hot Process
Hot process (HP) process soap making is the process where soap batter is made by mixing fats and oils with a lye-water solution until trace is achieved, just the same as in the cold process method of making soap. However, in the hot process soap making method, heat is added to the soap batter after trace by warming it on a stove or by pouring the soap batter into a crock pot. After approximately one hour, when all of the soap batter has boiled at a low simmer and has completed the gel phase, the soap is removed from the heat source and scents, herbs, and/or colorants may be added. The soap mass is then molded. Within a few hours, the soap may be unmolded, sliced into bars, and used. Hot process soap does not require any time to cure, to dry, or to harden.
Soap Making Process: Melt and Pour
The melt and pour (M&P) process of making soap involves using a pre-fabricated soap base, such as the soap base available from craft and hobby supply stores. These pre-fabricated soap bases often contain preservatives and stabilizers to provide a longer shelf life and superior meltability. The soap crafter cuts the soap base into cubes and melts the cubes in a double boiler or in a microwave. After the soap base is melted and is liquid, scents, herbs, and/or colorants may be added to the melted soap. Before the soap cools and hardens, it is poured into single-serving molds that are often specially designed shapes with meticulous details. Lye is not needed nor used in crafting melt and pour soaps.
Soap Making Process: Re-Batch Process
The re-batch process (RB) of making soap involves using cold or hot process soap shavings. The cold process or hot process soap shavings are combined with a small amount of water and are heated in a double boiler for approximately one hour, until they are melted and dissolved to form a thick, bubbly, viscous mass of soap. The mass of soft melted soap is removed from the heat and scents, herbs, and/or colorants may be added. It is then spooned into molds to cool and harden. After a week, the soap is removed from the molds and sliced into bars. Often, re-batched soap requires several weeks to dry, depending on how much water was used to dissolve the soap shavings.
Soap Making Process: Warm Process
For the warm process (WP) method of making soap, the soap maker begins by making soap with the cold process method but, instead of covering the molded soap with blankets, the warm process soap maker places the molds in a heated oven and incubates the soap at about 160° F for six hours. The molds are then removed from the heat source and allowed to cool slowly. After approximately 12 hours, the soap is removed from the molds and sliced into bars. Warm process soap is completely cured and free from lye as soon as it is cooled; however, warm process soap requires a few days to dry and harden. In warm process soap making, heat is added to complete the saponification of the soap, just as in hot process soap making. The difference is that hot process soap is boiled and warm process soap is not boiled, just warmed.
Sodium Hydroxide
NaOH; CAS Registry Number: 1310-73-2; Molecular Weight: 40.0 g/mol. Also referred to as lye, ascarite, caustic soda, soda ash, soda lye, sodium hydrate, and white caustic. It is a corrosive chemical that has a pH of 14, indicating it is a strong base. Sodium hydroxide is used in soap making to react with oils and fats to produce soap, frequently solid bars of soap.
Storage of Soap
Soap should be stored in a cool area that is dry, out of direct sunlight, and well-ventilated. While stored, soap should be labeled with its batch code to properly identify it and to differentiate it from other soap batches.
The practice of superfatting involves adding an excess of oils/fats to the soap batch beyond those calculated to completely saponify with the lye. For instance, if 5% superfat is desired, the amount of lye is first calculated to completely saponify the oil/fats, and then 5% more oil/fats are added to the recipe.
Term used to define the moment of cold process and hot process soap making when the soap batter thickens and becomes viscous due to the onset of saponification. Trace is determined when a spoonful of soap batter dribbled back into the soap pot leaves a "trace" and remains visible on the surface. Likewise, trace may be determined when a spoon moved through the soap batter leaves a "trace" or distinguishable trail on the surface of the soap batter.
Refers to something that readily becomes a vapor at a relatively low temperatures. Most essential oils, used to scent soap, are highly volatile.
Volcano Effect
When making lye-water solution, if water is poured onto lye, the top layer of lye dissolves and releases heat. A hard crust forms on top as the temperature quickly rises and water evaporates. The lye on the bottom remains dry and un-dissolved. As more water is added to the lye mass, the top lye continues to dissolve and a thicker crust is formed and more heat is released. Pressure builds underneath the crust until enough pressure ruptures the crust and forces un-dissolved lye, partially dissolved lye, hot steam, and water to spray up, resembling a volcano. Therefore, never add water to lye; always add lye to water.
Waste Disposal
Proper waste disposal involves following the supplier's instructions found on the MSDS for each material. Also, soap makers may contact a recycling center to ask if it will accept old essential oils, fragrance oils, rancid base fats, fixed oils, curdled soap batches, and etc.
Workplace Safety
Workplace safety when making soap involves having ingredients properly labeled and stored, maintaining a clean, orderly, well-lit, and well-ventilated work area for making soap, restricting the access of children and pets to the storage and work areas, having easy access to personal protective equipment, a telephone, a fire extinguisher, and running water.

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