Ghost Swirl Soap Revisited. FAQs about High and Low-Water Soap Design.

It’s almost exactly five years since I made my first Ghost Swirl soap. I made it for a soap challenge and since it garnered a lot of interest I wrote a quick blog post about it in September 2015. You can read my first Ghost Swirl post here.

Since then people have asked me lots of questions about it. And since the Ghost Swirl in all its simplicity still seems to fascinate soapmakers I think it might be time to recap and answer some of the most common questions about the Ghost Swirl.

The beginnings of the Ghost Swirl Soap

I made the first Ghost Swirl soap with a very specific goal in mind. I wanted to make a deliberate design of contrasts achieved purely by using different water concentrations and managing heat. I.e. I used no colourants at all – neither added to all of the batter or to parts of it. All that went into the soap was a master-batched mix of oils plus water and sodium hydroxide. Five years later I still make my Ghost Swirl soap like that.

For my original Ghost Swirl design I divided oils and sodium hydroxide each into three equal parts. For each of the three batters I then calculated water based on the weight of the sodium hydroxide. I made two low-water lye solutions with water at 1.4 x NaOH weight and one high-water lye solution with water at 2.4 x NaOH weight.

Here’s an example of what that could look like:

As you can see the ratio of oil to NaOH is the same in all the batters. It’s only the amount of water that differs.

Once everything was room temp and I had blended my three batters lightly I used two dividers to divide my mould into three lengthwise compartments. I then poured the high-water batter into the middle compartment and the low water batters into the side compartments.

After that I used a skewer to make tight swirls from side to side across the mould.

When I was done swirling I placed the mould in a 60C (130F) oven for a couple of hours. When the soap had cooled down completely I cut the log horizontally – and inside was a deliberate design of contrasts – without any colourant.

Why does it work?

It works because the high-water soap will go through full gel phase and the low-water soap won’t. Soap that has gone through full gel phase typically looks different from soap that hasn’t, hence the contrasting look.

High-water soap goes through gel phase at a lower temp than low-water soap. In my 60C oven situation the low-water soap is saponified quickly without ever reaching full gel phase. The high-water soap goes through gel phase more slowly and is kept at gelling temp both by the heat generated by the saponifying low-water soap and later on by the oven heat.

But gelled vs. non-gelled soap is only one part of the contrasting visual effect. Typically you also get a distinct translucent/dark outline where low-water soap borders on high-water soap. You see that clearly in the pic above of the first Ghost Swirl soap. Exactly what causes the dark outlines I don’t know. But because the low and high-water soaps are saponified at different rate they heat up, cool down, expand, and contract at different rate. There will be significant push and pull in those border areas throughout saponification.

Mostly the gelled high-water soap will look darker than the ungelled low-water soap. But sometimes the effect is the opposite; the fully saponified high-water soap actually looks lighter. Again, I don’t know why this is but I’m guessing it might be either a case of minute glycerine rivers or a case of ‘frostbite’; crystallization due to cool temperature. Read more about crystallization here.

That’s a quick recap on the method. Now let’s look at some frequent questions about the Ghost Swirl.

With lye solutions of different strength, won’t some parts of the soap become more lye heavy than others?

No. If you check the table above you’ll see that the ratio between oil and NaOH is the same throughout the soap. It’s the ratio of NaOH to oil that determines superfat/excess lye, not the amount of water in the soap. It’s quite important to note that we’re not using more of the same strength lye solution in the high-water soap. Instead we’re using a weaker lye solution (same amount of NaOH but more water).

Dividing everything into three seems like a lot of work – and containers to clean. Can’t I just make one batter and add more water to part of it?

Yes, you can. However, adding water to soap batter can cause some unwanted surprises. I’ve done it myself with instant heavy trace as a result. That might not be a bad thing – except if you are planning a tight, fine, fluid swirl. When blending the batters separately I’ve often had the high-water soap thicken up faster than the low-water soaps and I’ve heard of others having the same experience.

It’s interesting because it seems counter-intuitive. You’d expect the extra water to slow things down rather than the opposite. My guess is that it’s about temperature. Working with cool lye solution means that a larger volume of solution (more water increases volume) initially cools down the oils more and causes the mixture to thicken up a bit.

So, if you’re planning to add water to batter you’ll need to monitor temperature and make sure that the water you add is nice and warm – at least as warm as the batter is at that point.

Do I have to make three parts/batters and pour between dividers? Can’t I just choose any division and any swirl I like?

Yes, you can. But as you plan your design you should consider that this technique gives you subtle visual contrasts in the cured soap. Unless your swirl – or whatever pattern you decide on – has a deliberate look to it your soap might just end up looking like it was unevenly blended.

I like to do some type of ‘Taiwanesque swirl’ because that way I can make a deliberate, orderly pattern. Also, the pattern on the surface gives a good idea of what the pattern inside looks like and I really like that. But I’m sure there are lots of other options too for making cool, contrasting designs. Just use your imagination.

Can I use colour and fragrance with this technique?

Sure. My regular Ghost Swirl soap is free of colourant and fragrance. But if you add the colour and fragrance to your oil ‘masterbatch’ you’ll be able to create contrasting designs with water and heat. Just remember that this technique is about creating contrast by manipulating water content and temperature, not by adding different colourants to different parts of the soap. You can make exquisite designs e.g. by swirling uncoloured soap with soap coloured with titanium oxide, but that’s a different technique.

It’s worth keeping in mind, as always, that fragrance can accelerate trace and discolour soap. A very dark vanilla brown is likely to make subtle Ghost Swirl contrasts harder to see. And for fine, fluid swirls you don’t want the batter to thicken up too fast.

My oven doesn’t have a setting as low as 60C (130F). What do I do now?

I ovenprocess at 60C because it’s a handy way of making sure both that the soap is kept warm and that it doesn’t become too warm. Because I keep the oven switched on the thermostat kicks in and stops heating if the soap should start heating the oven rather than the other way around. I.e. the thermostat offers a bit of overheating protection.

But not having an oven is not a big deal. You just need to make sure that the high-water soap gets warm enough to gel. If you do like I do and pour the high-water soap in the centre of a log mould, the low-water soap on the edges will help heat up the high-water soap in the middle. If you insulate the mould with towels and blankets you’re very likely to get the high-water soap to gel nicely without ovenprocessing.

Just make sure you don’t let the soap get too hot. Once the soap reaches temps beyond 70-80C the low-water soap will gradually start to gel and you want to avoid that in order to maintain contrast.

Won’t the visual contrast between high and low-water soap fade as the soap dries during cure?

Yes, it will. Freshly cut the gelled high-water soap typically looks quite dark, even if the oils used where light in colour. As the soap cures and dries the colour will appear a lot lighter. But the visual contrast between gelled and ungelled soap will still remain and the outlines between high and low-water soaps will also remain.

With the difference in water content, won’t some parts of the soap warp more than others during cure?

Yes. During cure high-water soap shrinks and warps much more than low-water soap. If the design has relatively big solid portions of high and low-water soaps respectively you’ll notice the difference in shrinkage. That’s yet another reason to do a tight swirl or pattern where high and low-water soaps alternate frequently. The more stable low-water soap will help the bar keep its shape without edges and cut surfaces pulling in too much.

Even before cure the low-water soap helps steady the soap log; in my divider design the low-water soap along the edges makes unmolding and cutting easy as it protects the softer high-water soap in the middle.