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Stearic acid (stearin)

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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 (mainly beef, about 30%) and some vegetal (in smaller percentage, although cocoa and shea butter can contain up to 48%) fats and oils.

Stearic acid as we use it in candlemaking, in powder form

In candlemaking, the terms "stearic acid" et "stearin" are interchangeable and refer to the same product

Chemically speaking though, stearic acid is a component of stearin.

chemical formula:C18H36O2
melting point:around 158°F

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 compound 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, Chevreul invented a new substance named stearin (from the Greek "stear", which means tallow). Recent researches led to the development of a vegetable based substitute for stearin, until then always produced from animal fat. This vegetable substitute, which is gaining popularity among candlemakers, is primarily extracted from coconut oil (or palm oil).

Using stearic acid in candles

Michel-Eugène Chevreul

In the candlemaking world, stearic acid is available as a powder or pellets, has a whitish color and feels a bit greasy to the touch. Its melting point is around 158°F.

We use it primarily:

  • to raise the melting point of the paraffin wax it gets mixed with (logically, one part paraffin wax with a melting point of 130°F blended with one equal part paraffin wax with a melting point of 149°F results in a blend whose melting point averages 140°F). Adding a substance with a high melting point - like stearic acid - 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. Stearic acid can act as a hardener,
  • to make the candle burn longer (due to the fact that the melting point is higher).
Warning
Stearic acid 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, use Vybar instead.

The proportion of stearic acid you should use depends on the effect or result you're looking for. As a hardener, the common proportion is 3 teaspoons per pound (450 grams) of paraffin wax.

Used in higher proportions, stearic acid will opacify the wax, thus the finished candle too. In even higher proportions, a crystallization of the candle surface may appear.

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