How to Colour Handmade Soap with Mimosa Hostilis Root Bark

Soap makers know this bark as tepezcohuite. Its tannins give bars a natural brown colour, often with a pink or purple cast, without synthetic dyes, and the powder adds a light exfoliating texture. Here are three ways to use it.

Method 1: powder at trace (cold process)

This is the simplest method.

1. Measure about 1 teaspoon of powder per pound (450 g) of soap, the usual starting rate for powdered colourants. Use less for a pale tint.
2. Mix the powder into about three times its volume of a light oil until no lumps remain, the dispersion ratio soap suppliers recommend. Dry powder dropped straight into the batter clumps and leaves dark specks.
3. Stir the mixture into your soap at light trace, then pour as usual.

Method 2: oil infusion

For colour without specks, infuse the bark instead.

1. Cover shredded bark with a liquid oil from your recipe, such as olive oil.
2. Keep it warm for a few hours, or leave it in a sealed jar for several weeks, shaking now and then.
3. Strain through a fine cloth and use the oil as part of the oils in your recipe.

Method 3: water infusion

Simmer shredded bark in distilled water, let it cool completely, strain it, and use it in place of the plain water for your lye solution. This is the least predictable method, because lye changes many plant colours.

Melt and pour

Disperse a small amount of powder in a little glycerin or alcohol first, then stir it into the melted base. Fine powder can settle, so pour at a lower temperature and stir until the base starts to thicken.

What to expect

• The colour will shift. Cold process soap is strongly alkaline, and natural colourants can change shade as the soap cures. Judge the result after four to six weeks, not on the day you pour.
• More is not better. Too much powder makes a scratchy bar and can tint the lather. As one supplier puts it, the bubbles should stay white.
• Make a test batch first. Results depend on your oils, your water and your bark.

Which method should you choose?

If this is your first batch with the bark, use Method 1. It takes five extra minutes, and you can see straight away how much colour a teaspoon gives in your recipe.

Amounts for common batch sizes

These follow the starting rate in Method 1. Scale down for a pale tint.

Take the dispersing oil out of your recipe total, so the batch is not thrown off balance.

Fixing common problems

Dark specks or streaks. The powder went in dry or was not mixed smoothly. Next time work it into the oil with the back of a spoon until it looks like thin paint, and add it through a small sieve.

The colour changed while curing. That is normal with plant colourants in cold process soap. Keep one bar from every batch and write the amount on it. After three or four batches you will know what your recipe does.

The bar feels scratchy. There is too much powder in it. Halve the amount, or switch to an oil infusion for colour without texture.

The lather is tinted. Again, too much colourant. Reduce it until the lather stays white.

The colour is weaker than you hoped. Add a little more powder next time, or combine methods: infused oil for the base colour and a small amount of powder at trace.

Exact amounts for an oil infusion

Herbalists infuse dried plants at a ratio of 1 part plant by weight to 5 parts oil by volume, and it works well here. That is 20 g of shredded bark for every 100 ml of oil.

Start with a little extra oil, because the bark holds on to some of it when you strain. Keep the jar gently warm in a pan of water for four to six hours, or leave it sealed in a warm place for several weeks. Strain it through a fine cloth and weigh the infused oil as part of the oils in your recipe.

Why the colour is never quite the same twice

Soap suppliers say plainly that botanical colourants give unpredictable shades, and that the same recipe can come out differently from one batch to the next. The cause is the lye. Fresh cold process soap is strongly alkaline, and a high pH makes many plant colours shift. With this bark, expect a brown that can lean pink, tan or grey depending on your oils and how much you use.

Three habits make the result repeatable:

• Weigh the colourant as well as measuring it by the teaspoon, and write the weight down.
• Change one thing at a time. A new oil, a new amount and a new method in the same batch tell you nothing.
• Keep a cured bar from every batch with the details on a label. It is the only colour chart that matches your recipe.

How to tell you have used too much

The test suppliers recommend is simple: the lather should be white. Wash your hands with a cured bar. If the bubbles are tinted, there is more colourant in the soap than it can hold, and it may mark washcloths. Use less next time, or move the colour into an infusion.

Looking after the colour

Cure bars somewhere cool and airy, out of direct sunlight, and store finished soap the same way. Plant colours soften over time, faster in bright light. Wrapped bars kept in a drawer hold their colour longer than bars left on a sunny shelf.

Quick answers

Can I mix it with other natural colourants? Yes. Soap makers often pair it with clays to shift the shade. Change one thing at a time so you know what caused the result.

Does the kind of oil in my recipe matter? It affects the final shade. A recipe heavy in dark green olive oil gives a different brown from one built on pale oils.

If I sell my soap, what can I say about it? Describe the colour and the ingredient, and avoid claims that it treats a skin condition. In the United States a product sold with treatment claims can be regulated as a drug. The FDA explains the difference here.

Safety

Follow normal lye safety: gloves, eye protection and good ventilation. Patch test finished soap before regular use. Our bark is sold for dyeing, soap making and external cosmetic use only.

Root bark powder is the easiest form for Method 1. Shredded bark is the better choice for infusions.

More guides: how to dye fabric with the bark and whole, shredded or powder: which form to buy.

Usage rates are general soap-making starting points, so make a test batch first.

Sources

• Natures Garden: colouring cold process soap
• The Nerdy Farm Wife: herb infused oils and the 1:5 ratio
• FDA: is it a cosmetic, a drug, or both?