Cold Process Soap- Rainbow Technique

I started working at The Soap Kitchen in December 2018, I come from a cosmetic manufacturing background having worked for 25 years/since I was 21 in the industry. I have worked in a variety of roles; on a production line putting caps on eyeliner pencils, to manually capping foundation bottles, quality control, analytical laboratory testing, packaging technologist and now soap manufacturing!

Sonia- Deputy Creative Team Leader

Sonia’s First Cold Process

I was asked to test a new essential oil in cold process soap to see if it would react with lye, so as I am new to soap making, I looked up our tried and tested basic cold process soap recipe and have detailed it below.  If you have not made cold process soap before this is a great formulation to use. For future makes I will refer back to this recipe, so it’s a good one to bookmark!

For more nervous novice soap makers, we do also run workshops throughout the year which are a great opportunity to learn with an experienced soap maker. For more info click here

Basic Cold Process Recipe

You Will Need:

  • Two good sized stainless steel or enamelled saucepans.
  • A heat-proof glass measuring jug or plastic jug able to withstand boiling water.
  • Accurate kitchen scales.
  • A balloon whisk & rubber/wooden spatula, or similar.
  • A mould to pour the liquid soap into whilst it sets.
  • Eye and hand protection (safety glasses and rubber gloves).
  • A blanket or large towel.



How To Make:

Step One

  • Make sure you have all the ingredients and equipment listed above BEFORE you start, weigh them out into suitable containers ready to use.
  • Always wear safety goggles/glasses and use protective gloves when soap-making to avoid injury from spills and splashes.

Step Two

  • First choose your mould. Traditionally, soaps are made in silicone lined wooden moulds, but a cardboard box lined in a similar way is fine or you can use a silicone cake-baking mould, as they are usually lye and heat-resistant. Many forms of plastic kitchenware will be suitable and may also not need lining, such as ‘tupperware’.
  • If choosing a traditional lined wooden mould & lining paper, ensure the paper is not cut or holed in any way below the top of the mould. It must be folded into corners etc. to ensure there are no leaks.

Step Three- Making The Lye

  • Measure out 340g of cold clean water into a jug. Weigh (accurately) 125g of sodium hydroxide beads (or pearls) into a suitable container. Carefully add the sodium hydroxide to the water, and whisk, stirring all the time. Be careful not to breathe the vapour that is initially given off, so hold your breath and stir until all the sodium hydroxide has dissolved and there are no lumps stuck to the bottom of the jug.
  • The solution (now known as Lye) will heat up to nearly 200°F and will need to be left to cool. Place the jug in a large bowl of cold water, being careful not to ‘float’ it, so basically make sure the lug is submerged and not simply floating on top of the water!)

Step Four- The Oils

  • Meanwhile, measure out exactly 284g of coconut oil and 170g of palm oil into one of the saucepans (the smaller if there is one) and gently melt it on the stove. Don’t overheat it, just melt it. When there are tiny pieces of solid oil still left to melt, turn off the heat and leave until completely liquid.
  • Whilst the solid oils are melting, measure out 454g of olive oil (pomace grade is best) into the other saucepan (this will be the soap-making pan). If adding optional preservative, add it to the olive oil now.
  • Once melted, pour the combined coconut and palm oils into the olive oil and mix them all together.
  • Then slowly and carefully pour the lye into the oils, and start stirring with a balloon whisk to ensure the mixture all starts to chemically react and combine.
  • You should stir the mixture fairly briskly. You will notice the solution start to turn more opaque and as the minutes pass it will start to thicken.

Step Five- The Trace

  • The stage in the process you have to wait for is known as the ‘Trace’. This is when you can drizzle the mixture from the whisk onto the surface of the solution and it leaves a visible trace before sinking back into the rest.
  • If adding colour with ultramarines, oxides or food-safe water soluble powders etc., make them up in a little water and add them now (just before or at the trace).
  • If adding essential oil/s, add them at ‘the trace’ after any colour and stir in well.
  • Once everything is added and the mixture traces simply pour it into your lined mould.
  • Cover the mould with something like a cardboard sheet to prevent anything touching the surface of the soap whilst it’s setting.
  • Insulate with old towels or a blanket and leave at room temperature until the soap has solidified. With a small batch like this example, this should be no more than 24 hours. Larger batches can take longer.

Step Six- Cutting

  • Once set and cool, remove the soap from the mould and remove any lining paper from the soap. At this stage it should still be soft, so it’s time to cut it into blocks, using either a metal scraper, a knife, or a wire cutter. If it appears too soft to handle however you should leave it for 2-3 days and try again.
  • Leave your soap ‘curing’ at room temperature for typically at least 3-4 weeks, preferably on a sheet of uncoloured absorbent paper allowing air to circulate around each bar or Curing will allow the soap to lose excess moisture and become harder.

Rainbow Technique

So back to my soap, I thought that this would be a good opportunity to try a different technique, using colours that I knew worked in cold process soap. I decided to split the soap mould into 4 sections. I did this by putting 3 dividers along the length of the silicone mould using thick plastic but cardboard would also work. Using the basic recipe as above, I made up the lye and oil mixture, once the soap had reached trace (step 5), I added the fragrance and divided the mixture by eye into 4 separate plastic jugs.

In each of the jugs I added a different colour and mixed well.  With Alix’s help stirring the jugs and helping to hold my wobbling dividers, I managed to pour one colour into each section a little at a time, repeating until all the mixture was used. After carefully removing the plastic dividers I used a cocktail stick to swirl the top of the soap together before it thickened too much.

Overall, it was quite fiddly and an extra pair of hands was useful,  the trace set quite quickly and my memory is of panic and relief that it hadn’t been a total disaster!

I have stopped worrying so much now and I am becoming far more relaxed about making soap, I’m always looking for new challenges and I have a long list of techniques I plan to try out.  So give it a go if you are considering trying it out.

For those of you who missed it, here is Sonia’s soap fresh after the pour!


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