I was doing some research on cream soaps tonight. Cream-style shave soaps were coming up in my searches, because cream-style shave soaps are, for all intents and purposes, basically a type of cream soap.
Anyways....
Here is an interesting tidbit from the American Perfumer magazine from 1912 that relates a bit to this discussion. The author uses rather dense language, but I think you'll get the gist. Notes in brackets [ ] and underlining are mine.
Excerpt from WHITE SHAVING SOAPS, by H. MANN, in The American Perfumer and Essential Oil Review, Vol. 7, March, 1912, pp 56-57.
"...We distinguish shaving soaps made according to the warm process, the semi-cold and the cold process, also those that are produced by means of the plodder [mechanical mixer]. We also distinguish solid and semi-solid shaving soaps, also shaving soaps in cream form and, moreover, liquid shaving soaps....
"The requirements that a first-class shaving soap must meet are, that it must produce a thick lather, that will not dry in, that it is, moreover, free from irritating, that is to say, biting effect on the skin, consequently perfectly neutral and that, nevertheless, softens the beard in a proper manner and prepares it for the operation of the razor. With some trade knowledge and care, all these provisions may be fulfilled.
"We take, therefore, as the foundation for such a [solid] soap, a pure, fresh, beef-tallow, because the soap this yields gives a smooth, thick lather; as this alone would, however, not suffice, we add to it, ... about one-third of the quantity of tallow in Cochin cocoanut oil to which some manufacturers add a small percentage of castor oil, which, however, cannot be exactly recommended, because the so-called cold saponification of castor oil should be, wherever possible, avoided.
"For the saponification of the fats, we take about one-half soda lye, of 37° Baume [31.2% NaOH solution] and half potash lye of 35° Baume [32.7% KOH solution]. To prevent any possible excess of alkali, we add to the soap, before pouring it into the frames, about 2 per cent, of the finest washed and pulverized chalk..."
Given all the talk about whether or not to add clay to shave soap, I thought it was interesting to see this addition of chalk (calcium carbonate). They are using the chalk, not as lubricant, but as an additive to prevent excess alkalinity. The way these soaps were made, excess lye was a definite possibility. But the chalk would also function as a slip agent as well.
My husband thinks I'm crazy. But this seems to be the place for me from reading the forums here.
lol I'm not really experimenting so much for hubby since he's happy with my formula just as it is, but I'm doing it mostly for myself because I'm a curious soap-maker who wants to see how much I can improve on the ease of lather factor. And also because the troublemaking wet shaver dudes challenged me to try reformulating without clay since many of the major brands don't have clay in them (and the crazy, mad-scientist soapmaker in me just couldn't resist a challenge such as that!). lol 
