Stearic acid (stearin)
Stearic acid (also called stearin or, to keep it simple, octadecanoic acid) is one of the saturated fatty acids present in animal (and vegetal) fats and oils.
Where candlemaking is concerned, the terms stearine and stearic acid are interchangeable and indicate the same product.
Chemically speaking, stearic acid is a component of stearine.
In the Nineteenth century, a chemist named Michel Eugène Chevreul discovered that animal tallow (in this time still used to make candles) wasn't a single substance but a coumpound of two fatty acids, stearic acid oleic acid, combined with glycerin to form a neutral, non flammable substance.
By removing glycerin from the tallow compound, Chrµevreul invented a new substance named stearin (from the Greek "stear", which means tallow).
Recent researches led to the development of a vegetal based substitute for stearine, until then always produced from animal fat. This vegetal substitute, which is gaining popularity among candlemakers upon the animal counterpart, is mainly extracted from coconut oil (or palm oil). For information, cocoa butter is made of 35% (!!!) stearic acid.
How and when to use Stearic acid?
In our domain, candlemaking, Stearin (that's how I'll call it from now on) is available in powder or granulated form, has a pure white color and feels a little fat when you touch it. Its melting point is 158°F.
It is mainly used:
to raise the melting point of the paraffin it gets mixed with (logically, one part paraffin with a melting point of 130°F mixed with one equal part paraffin with a melting point of 150°F results in a mixture whose melting point averages 140°F). Adding a substance with a high melting point - like stearin - to paraffin has a tendency to raise the average melting point of the mixture,
on the contrary, to lower the melting point of a high melting point paraffin,
to give the colors a pastel shade,
to "harden" the candle. Stearin can act as a hardener,
to make the candle burn longer (due to the fact that the melting point is higher).
Stearin should not be used in combination with rubber or latex molds because it might "eat them up" (it is an acid, after all). If you're planning on using rubber molds, replace stearin with Vybar.
The proportion of stearin you will use depends on the effect you're looking for. As a hardener, the common proportion is 3 teaspoons per pound (453 grams) of paraffin.
Used in higher proportions, stearin will opacify the wax, thus the finished candle too.
The Nebraska Beef Council (www.nebeef.org), has very detailed information about stearic acid.
Animal fat contains 9 to 12% stearic acid