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According to Roman legend, soap was discovered after a heavy rain
fell on the slopes of Mount Sapo (the name means Mount Soap in Latin). The hill was the
site of an important sacrificial altar and the rainwater combined with the mix of ash and
animal fat around the altar's base. As a result of this fortuitous coincidence, the three
key components of soap were brought together: water, fat and liquid potash leached from
ashes. As the mixture trickled down to the banks of the Tiber River, washerwomen at work
there noticed that the mysterious substance made their job easier and the wash cleaner.
Over the centuries the basics of soapmaking have remained essentially unchanged from the
Roman prescription. To this day soap is being home-made much as it was in ancient Rome:
out of a traditional or commercial form of potash --usually referred to as lye -- rainwater and some form of oil or fat. Even commercial soap is
manufactured by much the same process. Other than obvious differences in the scale of the
operation and the use of automated equipment, the chief innovations in the commercial
product are the substitution of the sodium hydroxide (caustic soda) form of lye for potash
based on wood ash and the frequent use of a variety of vegetable oils and animal fats
combined.
One substance, many varieties
Although, by definition, every soap is made by the saponification (chemical combination)
of potash or potash substitute, water and fat, one soap will differ from the next
depending on the kind of fat, the kind of potash and how much of each is used. Potash made
from wood ash, for example, produces soft soap, so-called because of its jelly-like
consistency. In contrast, soap made from sodium hydroxide will be hard. Soaps containing
coconut oil tend to lather well in cold water but may have a drying action on the skin.
Superfatted soaps, such as castile, that contain large amounts of unsaponified fat are
particularly gentle and make excellent toilet soap.
Soap can be altered in consistency and appearance to serve different purposes. Jellied
soap for doing the washing-up is obtained by slicing off shavings of hard soap and boiling
them in water until they dissolve; about 125 grams of shavings per litre of water should
be used. To produce soap flakes for laundry use, grate any ordinary hard soap, then add a
few tablespoons of borax to improve its water-softening ability and quicken sudsing
action. The preparation of liquid soap is more complicated. It is generally based on
vegetable oils rather than animal fats and requires the addition of glycerin and alcohol
during the soapmaking process, followed by filtering. If you want soap that floats on
water, gently whip the warm soap solution with an egg beater just before pouring it into
moulds; when the soap hardens, the trapped air bubbles will provide the necessary
buoyancy.
The basics are the same no matter what the soap
The three ingredients needed to make soap -- oil or fat, water and lye
-- are all readily available. Lye in the form of sodium hydroxide (caustic soda) is sold
as dry crystals in many supermarkets and hardware stores, while lye in the form of potash
can be made at home from wood ash. All types of lye are highly caustic substances. Fat for
soapmaking can be almost any pure vegetable oil or animal fat, from reclaimed kitchen
grease to castor oil. The water should be soft. If you are in a hard-water area, treat the
water with a commercial softener or add a few tablespoons of borax to it. You can also
collect rainwater and use it in soapmaking.
The following basic equipment is needed for home soapmaking:
A sturdy container to hold the caustic
soda solution.
A 2-litre glass jug or wide-necked bottle with a plastic lid will do. Punch two
holes on opposite sides of the lid for pouring the solution over the oil or fat later on.
A 10- to 12-litre saucepan to hold the oil or fat and caustic soda solution.
A wooden spoon to stir the solution.
A dairy thermometer that is accurate to within half a degree in the 25-50ºC
range. For convenience you may want to have two thermometers.
Moulds for the soap. Old baking dishes or shallow wooden boxes are practical
containers for large amounts. Prepare the moulds by lining them with clean, damp cloth,
plastic or greasing them with a commercial petroleum jelly.
Insulation to keep the soap warm after it is poured into the moulds. Cardboard,
newspaper, towels or an ordinary blanket can be used.
Prepare the caustic soda solution first and allow it to cool. To make the solution,
pour cold water into an enamelware pot, then add the crystals slowly while stirring the
water steadily with a wooden spoon. The reaction between the caustic soda crystals and
water will generate temperatures over 90ºC. The container can be placed in a large basin
of cold water to hasten cooling. Once the solution has been cooled, pour it carefully into
the 2-litre glass container. If you are going to use animal fat for your soap, you should
also prepare it in advance to allow it to cool down (the rendering process takes place at
well above the temperatures needed to make soap).
Oils or fats can be refrigerated and then brought to soapmaking temperature by warming in
a basin of hot water. The type of material oil or fat, caustic soda and water that should
be combined depend on the particular type of soap being made. The standard recipe calls
for 3 kilograms of beef fat, 1.5 litres of water, and 410 grams of caustic soda crystals.
If using vegetable oil, quantities are 4.5 kilograms, 1.8 litres and 585 grams
respectively.)
Saponification is the chemical process by which soap is
formed from its three main ingredients. In order for saponification to take place, the
temperature of the caustic soda solution and fat has to be carefully controlled. The
simplest method is to bring both the caustic soda and the fat to a temperature of 35-37ºC
before mixing them together. Some experts recommend that the fat be at a higher
temperature than the caustic soda: about 52ºC for the fat and 34ºC for the caustic soda
when beef tallow is used, 28 and 23ºC when lard is used, 41 and 28ºC for half lard, half
tallow.
Occasionally, saponification does not take place and the
soap mixture separates into a top layer of fat and a bottom layer of lye solution.
Generally, the mixture can be reclaimed by heating it to about 60ºC while gently stirring
with the wooden spoon. Then remove from the heat and keep stirring until the mixture
thickens into soap. To test your solution, take some in the spoon and let a few drops fall
back onto the surface of the soap; if the surface supports the drops for a moment or two
before reabsorbing them, the soap is ready for the moulds. Place the moulds in a warm
place and leave for 24 hours or so for the soap to set. If you have used lined containers,
the lining can be lifted out and the soap sliced into cakes.
Soap & Bubbles has recipes for soaps and bubble
blowers.
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