The Challenge: Make Soap
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FIRST PUT ON YOUR PROTECTIVE GLOVES, APRON AND GOGGLES
1. It's advisable to do this first step outside. Stirring continuously, gradually
add the sodium hydroxide carefully to 200cc (6.75 fl. oz.) of cold distilled
water in one of the mixing bowls. Never add the water to the pellets! Avoid
inhaling the fumes while doing this. The temperature of the solution will
rise as you continue stirring, until all of the solid has dissolved. Let
this solution cool to around 45° C (113°F).
2. Next weigh out the
vegetable fat, olive oil and coconut oil into one of the mixing bowls. Warm
the mixture gently by standing the bowl in hot water, stirring all the time,
until it reaches 45° C (113°F). Don't let the temperature of this mixture
rise above 50°C (122°F).
3. When the sodium hydroxide solution and the mixture of fat and oils are both at
the required temperature, pour the former slowly into the latter and stir
thoroughly for 15 minutes with a spoon.
4. Saponification doesn't happen instantly! With some vegetable oils it
can take weeks to complete, but you should see something
happening after 5 or 10 minutes; the mixture should start to thicken up.
The process involves several stages, the first of which is called "tracing".
If you let the mixture run off the back of the spoon into the mixing bowl,
you should see that the soap that's formed floats on top; in other
words, it leaves a "trace" on the surface.
The time it takes to trace depends on the particular fats and oils you use;
the lighter the fats or oils, the longer they'll take to trace.
Stir the mixture gently
for 5 minutes or so, then leave it for 15 minutes, before stirring for a
further 5 minutes... and so on, until after about an hour the mixture
thickens to the consistency of custard.
All this may just seem like cooking, but there's some serious chemistry going
on here. As saponification proceeds, the oils, fat and caustic soda react
together, heat is generated, water evaporates and the soap begins to harden.
5. If you want fragrant soap, stir in the essential oil or lemon juice at this stage.
6. Pour your traced mixture into the plastic molds and put them in a warm, dry place.
7. Clean up your work area immediately and thoroughly wash all of the utensils you've
used in hot soapy water.
8. After a week or so, your soap should be hard enough to remove it from the molds.
Put your rubber gloves on to do this! At this stage, it will still contain
some unreacted sodium hydroxide. To make it safe to use, stand it on newspaper
in the open air at room temperature for two to three weeks, after which
saponification should be complete. The longer you leave it, the better your
soap will be.
UNDER NO CIRCUMSTANCES SHOULD YOU USE YOUR SOAP UNTIL YOU'RE SURE THAT IT CONTAINS
NO UNREACTED CAUSTIC SODA! EVEN THEN, TO BE ON THE SAFE SIDE, ONLY USE IT
TO WASH YOUR HANDS; NEVER USE IT TO WASH YOUR FACE.
You might like to try to and improve on the above recipe by using different oils and fats,
or different reaction times. You could also add food colours to your soap
to improve its appearance. This is the way practising synthetic chemists
work, experimenting with different starting materials and reaction conditions,
until they get the result they want. So experiment away and have fun!