There were many challenges with this process. Regarding quality of the lather, I attempted to standardize this by, first of all, trying to use about the same wetness in the shaving brush for each soap. Then I swirled the brush on a given soap puck for about ten seconds. Then I lathered in a stainless lathering bowl for about ten seconds. Then using my fingers I transferred the resulting shave lather to a re-purposed yogurt cup, rinsed the tools and did the whole thing again for the next soap. This whole lather-making process was the first issue because I standardized the process rather than using the best process for a given soap to make lather. As a result, some of the lathers were a bit less pasty (more runny) than I might normally use.
I applied the lather from the yogurt cups to my face using my index finger, which, again, deviates from the normal process of applying lather with the brush. On a given pass, I would apply one soap on its allotted real estate, shave that area, rinse, and move on to the next area with the next soap. The finger-application method generally resulted in a more watery, more translucent application of soap; my normal brush-applied lather is opaque and creamy but not deep -- only a millimeter or so.
I did three passes during the evaluation; the usual ones: with, then across, and finally against the grain. When I was done, there was little difference, so I picked one of the soaps, took out a different razor and blade, and did a complete, full-face, three-pass shave. I was thinking that this would increase the opportunity for face abuse, and thereby highlight the differences in the areas that received six passes.
The good news is that I got a very close shave this morning!
The bad news is that the head-to-head comparison was useless. Although there are clear differences in the characteristics of the lather from different soaps when using a (more or less) standardized lathering process, the only outcome that matters is the quality of the shave.
Many wet shavers pay attention to various perceivable characteristics of a given shave lather, but in reality, given all the variables involved in just making that lather, it is very difficult to determine relative quality of the shaves.
This means that I need to give more thought to getting better, objective evaluations of shave soap outcomes. Perhaps I will write another article on this in the future.
For now, I am still the face of the guinea pig, and that face is red -- not from making too many passes, but crimson with embarrassment.