Thank you Lilian for finding that, this looks very similar the the shape and colour of the unknown white wax chalk I have the one that looks like pieces of glitter are in it. I have bookmarked this for future reference.
My little piece of wax chalk left over from the 60's is not a solid white, it is sort of transparent, but that really is not the right word, it is so precious that I am very sparing with it. When I was doing the tailoring course, we had to make a sampler which consisted of half a back of a jacket, so top half of the back so that we could fit a collar on, and I was using a dark grey piece of flannel and this wax chalk showed up beautifully. It is such a shame that certain things we have used and loved have totally disappeared - why when they worked so well.