Soap-making is a delicate process, but the ingredients used to make soap are fairly simple: oils, lye, water, fragrances, colorants, and other, optional additives. The fats and oils used in soap can be derived from either animal or vegetable fat. Typically, soaps made from vegetable oils are softer than those made with animal fat. The most useful oils for soap-making are fixed oils – oils that can be raised to a high temperature without evaporating. Fixed oils include a variety of base oils, such as olive, palm and coconut oils.
There are two types of fats used for soap-making: saturated fats and unsaturated fats. Saturated fats make a hard soap.
They commonly come in a solid form and must be melted prior to use; cocoa and shea butters are good examples of saturated fats. Unsaturated fats, like some vegetable oils, come in a liquid form, and are commonly used to make liquid soap. To use these fats to make bar soap, they must be mixed with saturated fat; the more saturated fat you use, the harder the bar will be.
Historically, lye (also called sodium hydroxide, potash, or caustic soda) was hand-extracted from wood ashes. It is now commonly found in many hardware and grocery stores. It is the ingredient that hydrolyzes the oils or fats, and turns them into soap.
The minerals and other additives in tap water make it less than ideal for soap-making. Therefore, it is best to use distilled, bottled, or spring water. There are two types of scent oils: essential oils and fragrance oils. Fragrance oils are man-made and contain alcohol, so they are typically avoided; the alcohol and other chemicals in the oil may be drying or irritating to the skin, and cause unforeseen problems with the saponification process, or ruin the soap mixture altogether.
Essential oils are more costly, and sometimes more difficult to find; however, a smaller amount is required (usually only a drop or two) and they retain their scent better because they are undiluted. Research oils thoroughly before use; some can be irritating to skin, or even toxic. Also, different amounts are required for different oils, because some will overpower others if the same amount is used for all.
Avoid potpourri, candle scent oils and other strong, commercially-made fragrances, as they often contain harsh chemicals that can be irritating to the skin as well. Whole or crushed herbs can also be used, but they will not give their full benefits in a first batch of soap; if you use herbs, the best thing to do is to rebatch the soap later, to extract the full benefit from the herbs.
Colorants can be purchased at a soap-making supply store.
There are also various other natural ingredients that you can use to color soap, such as powdered clay, cocoa powder, tea, paprika, saffron, or ratanjot. Avoid using fabric dyes, hair dyes, candle colorants, or paints to color your soap; even if they are labeled as “non-toxic,” they are not safe to have in contact with skin for prolonged periods, and they may dye your skin.
Some sources say that crayons can be added to soap for coloration, as long as they are made of stearic acid (most crayons made now are), but there is some debate on this topic; it is probably best to err on the side of caution, and avoid using them.
Depending on the oils used in the recipe, the resultant soap can be prone to spoilage.
Various preservatives can be utilized, such as vitamins E, C, and A, which are also great for your skin. These vitamins can be found in various oils. Sand or pumice can be added to the soap, to make it exfoliating. Also, some metals, such as titanium, silver, nickel, or aluminum can be added for antibacterial properties, and to make the soap bright white.