There are a number of images showing small sticks of sealing wax, presumably for applying directly to paper when writing letters.
What is not immediately clear is how wax is used when creating pendant seals that are attached to tags, tongues, and cords.
As noted by the Imprint Project, the Trinity College Cambridge MS R.14.37 manuscript contains a recipe that “when the wax mixture has solidified but is still warm, it should be ‘tossed’ between well-greased hands, rolled into a sausage, and sliced to form cakes.”
Maerten van Heemskerck’s 1529 portrait of Pieter Gerritsz shows another interesting detail. Next to his wood-handled seal matrix is what looks like a paper-wrapped packet of wax, surrounded by squares of paper. It seems to me that it would be convenient to have prepared wax slices packaged in this way, with bits of paper in between to prevent them sticking together.
My early experiments with cutting wax slices were frustrating. When the wax was still soft, I tried cutting it with a knife. The wax would stick to the knife and also deform, so it didn’t produce good slices. I also experimented with using wire to cut the wax, but the wires tended to break and didn’t cut as well as I’d hoped. I didn’t want to risk ruining a saw blade, but ultimately I found that a coping saw did a good job of cutting the hardened wax. It was melting as much as it was cutting, so gentle pressure and a vigorous sawing motion was required to cut slices without the risk of breakage. That said, the slices were still not the prettiest. In an attempt to start with the roundest log possible, I packed the soft wax in an oiled piece of PVC pipe and pushed it out once it had hardened (a few minutes in the freezer accelerated the process).
Once the slices were cut, I stacked them up with paper in between, and wrapped them in a larger piece of paper. I closed the seam of the wrapper with a melted bit of scrap wax, and closed the bottom of the packet similarly.
To use the slices, they can be held briefly over a flame to soften them. I made tongs to hold the slices safely during this process. The slices can then be sandwiched around a tag, or kneaded and molded in place.
There is definitely still a lot of experimentation to do with this method. I think that waiting for the ideal moment in the cooling process, when the wax is firm but not yet brittle, may be ideal for cutting good slices. Also using an oiled, sharp knife may work better than a saw. For a more anachronistic option, I suspect that an electric hot wire would do a good job of cutting the slices. In any case when the cutting method involves melting the wax, it is important to remove the slice quickly, before it solidifies again.