I’ve often been asked how the inverted stamp technique tops on my handcrafted soaps are made. A while ago I promised to write a tutorial with pictures about this so here we are.
The inverted stamp technique is a method of embossing the surface of soap. When embossing soap with a stamp you force an imprint into the soap. With the inverted stamp technique you do the opposite: you ‘pull out’ a mark on the surface of the soap – hence the name. I make no claim to have invented the technique; it’s been around as long as cold process soap has been made. But I have worked extensively with it and made it a defining design feature on several of the soaps in my standard line. It’s practical because it allows you to add interest and decor to soap tops while essentially keeping them flat for easy packaging.
The inverted stamp technique makes use of that phase in soapmaking when ongoing saponification causes the soap batter to go from runny emulsion to a solid state. Among soapmakers this phase is commonly known as ‘trace’, referring to the trace that is left on the surface of the thickening soap batter when touched. Unlike embossing with a stamp which typically happens when the soap is fully saponified and can be done any time over a period of several weeks or even months, the inverted stamp technique is a little more challenging in that it has a short window of opportunity – a minute this way or that can make a big difference for the final result.
So, the viscosity of the soap batter is crucial. The other important thing is the tool – or tools – used to emboss the soap. You can, of course, use anything you happen to have handy to make a mark in soft soap. I prefer to use thin steel wire for this because I feel it gives me more control than just the edge of a spatula or cookie cutter pushed into the soap.
Here’s how you do it:
You pour the soap at very light trace. In fact, you should pour as soon as your emulsion is stable. This is often the case well before trace. The benefit of pouring before trace is that you’ll be able to scrape out your bowl or pot into the mould without leaving any drip marks on the surface. Drip marks on the surface may seem slight when the soap is wet but tend to look a lot more accentuated once the soap has set.
Once the soap is in the mould you check the surface. If you managed to pour at emulsion you’re likely to be fine and can proceed to the next step. If you poured at trace and you have drip marks on the surface you’ll want to smooth them out. You can do it with a spatula, scraper or something else that produces a flat surface. Or, you can add a bit of extra texture with something that produces drag marks. For lattice tops I like to use this guide for chopping onions, but eg an Ashanti comb or afro pick could serve the same purpose:Now you’re ready to start ‘stamping’. If you had to smooth out drip marks on the surface you’ve got no time to waste and have to go right ahead. If you poured at emulsion and the soap is still very runny you need to wait for it to get slightly thicker. ‘Slightly’ is the operational word because for the best results you have to catch it at the perfect moment. If the soap is too runny you won’t be able to make a well-defined mark. If it’s too thick the marks will be over-defined, ie you’ll get jagged peaks where you pull out your wire. Under perfect circumstances I have time to wait for the soap to thicken up and I usually prod one corner with a stick to see when the mark is just the way I want it. As long as the soap is still runny it’s very forgiving; you can keep ‘backtracking’, making a mark in the same spot several times until it looks right.
Here’s the tool I used and another top made with the same tool holding it at a slightly different angle:
The inverted stamp technique of embossing soap can obviously be used for an endless number of designs depending on how skilled and artistic you are at bending wire – either on its own or in combination with other design techniques. One of the most popular designs using this technique is the lattice top with crossing diagonal lines making a wafer-like pattern on the top of soap. In the picture below you can see that the soap batter was already slightly too viscous when I made my lines. The ridges are of uneven height due to jagged peaks forming as the thickening soap begins to stick to the wire.
- I first pull my comb/onion chopping guide along the surface of the soap making drag marks parallel to the long sides of the mould.
- Then I grab my wire (the angular, u-shaped one in the pic above) and start making parallel marks diagonally across the mould. Keeping the distance between the marks and the angle constant is a bit of a challenge. My wire fits perfectly at an angle between the insides of my mould so I use the sides of the mould as a guide for the angle. To get the distance right I try to work rhythmically – on the beat.
- When I’ve gone down in the one direction I go in the other direction making marks down the length of the mould ending up with a diamond pattern. I try to keep the diagonal lines close together – to get as many diamonds as possible on the top of each bar.
To me a pretty lattice top on its own is quite striking and my personal preference is to do the inverted stamp technique on a background of one solid colour. But you can easily combine a lattice top with other design elements like colour and embeds:
I mostly work with log moulds, but the inverted stamp technique works well with slab moulds and individual moulds too. The larger the surface area the more you can show off the embossed designs eg by using several different embossing tools to create intricate combined designs. Note, however, that a large surface might take longer to emboss so make sure that you work with soap formula and fragrance that doesn’t thicken too fast.
Here inverted stamp lily pads are featured on their own and combined with cold process frog embeds:
Works nicely with individual moulds too:
Here the leaf tool was used to make single ‘prints’ on individual oval bars as well as to make a pattern covering the top of a log:
A curved scallop shape to suggest curly wool on the Lanolin & Lemongrass Merino Soap:
And finally a nearly perfect ‘squiggle’ execution on top of the Black Sheep Merino Soap: