Ghost Swirl Soap Follow-Up

The response to the un-coloured Ghost Swirl Soap that I posted about a month ago (you can read about it here) has been rather overwhelming. I’m humbled by all the positive comments and I’m very excited to see how other soapmakers have created truly exquisite soaps using this technique. It seems that my post has inspired quite a few to experiment and venture into new territory, and by their experiments they have learnt more about what can be achieved and how soap works. That’s great and it warms my heart.

I’ve also been asked a lot of questions about how a soap made of portions with differing water content will fare over time. Will the bars crack and break? Will the high and low water portions come apart? If the contrast is achieved only by different water content, won’t that contrast disappear as the water evaporates from the soap? Will the contrast disappear over time like partial gel circles sometimes disappear over time? Will the shape of the bars be distorted as the high water portions shrink more than the low water portions? What will happen to these bars in use, will one portion wear down faster than the other?

On Friday a month had passed since the soap was made and so I took some follow-up pictures to show what the soap looks like at this point in time. Now, many will argue that any good soap needs at least a six week cure and it’s true that this soap will continue to slowly shrink and lose water content over time. But water evaporation is by far the most dramatic in the first four weeks; i.e. what the soap looks like after four weeks is a good indication of what it will end up looking like after a year – especially as it contains no colourants that have the potential to morph, bleed or fade.

Not a lot of change has taken place. Those border lines between low water and high water soap are still very crisp and clearly defined and there is a definite difference in shade between low and high water soap. The shape of the bars is not distorted and the different portions don’t seem to want to part with each other and come lose. In fact, there’s so little change in how the soap looks that it’s a bit of an anticlimax 🙂

Now, why hasn’t a month of cure time had more effect on the way the soap looks? First of all let’s remember that the difference in shade in these bars was not only caused by different initial water content, but by different gelling behaviour. High water soap enters full gel phase at a lower temp than low water soap and we managed to manipulate the temperature so that it was high enough for the high water soap to enter full gel phase, but too low for the low water soap to enter gel phase. I.e. the high water soap went through full gel phase and the low water soap didn’t – at least not completely. When soap goes through gel phase its molecules re-arrange themselves to form a particular crystal structure. Among other things this crystal structure makes gelled soap appear more transparent than un-gelled soap. By being transparent it doesn’t reflect light like un-gelled soap does and therefore appears darker. Even though more water will evaporate from the high water portions than from the low water portions, the difference in internal structure will remain and so the appearance of contrast will remain.

But what about partial gel circles that sometimes fade away and disappear with cure? There’s a bit of linguistic confusion surrounding partial gel. To soapmakers partial gel typically means that uneven heat in the soap causes one part (typically the centre) to go through gel phase while other parts don’t reach gel phase. This results in uneven colour and shade sometimes regarded as unsightly. To chemists partial gel means that both gelled (‘neat’) and un-gelled (‘curd’) soap is present simultaneously at a molecular level in the soap as a whole (Kevin Dunn talks about this on p. 306 in Scientific Soapmaking) So, I suspect that partial gel areas that disappear with cure are truly partially gelled. I.e. the area has been warm enough for some crystal development to happen, but not warm enough for the soap in the area to fully crystallize. As water evaporates the appearance of contrast diminishes, but often the circles become visible again when you wet the soap.

With the evaporation of water the texture of the cut surfaces of the Ghost Swirl Soap has become a little more pronounced, but not drastically. Interestingly, the texture is mainly provided by the border lines between the low and high water soap. I haven’t used more than a tiny test sliver of the Ghost Swirl Soap yet so I can’t say much about how the bars will wear. But I would predict that if anything is going to wear down faster than something else it will be those border lines. I say this because that is what happened with the bars that I made for the glycerine rivers experiments. In both batches all the bars wore the same way: no perceivable difference between low and high water soap, but a definite groove forming along the border between the two:

So far, the shape of the bars looks much like it did to begin with. No distortion that I can see. This is probably partly due to the fact that water evaporation isn’t the only way that moisture is transferred: the low water soap bordering on the high water soap is likely to initially absorb moisture from the high water soap and so the moisture level is likely to even out to some extent during and shortly after saponification.

For those keen to be part of the action and follow the further developments of the original Ghost Swirl Soap first hand, a few bars of this first-ever batch are available on our webshop as of today – beautifully wrapped in suitably ghostly attire with hand-printed trim 🙂