In our workshop after learning how to coat evenly, applying the emulsion to 5mil (thousandths of an inch), we ended up with some extra emulsion. It appeared that there was not enough to properly coat a piece of paper, so with gloves on I poured this remainder onto a sheet of Strathmore Bristol and used my fingers to spread it around.
This actually worked better than I thought it might but there was one flaw. Spreading in this way resulted in a circle of emulsion that was very thick. This thickness meant that the fixer was not able to properly penetrate the emulsion, and that ring can now be seen as a brown stain. Looking a little more closely I can see numerous small pockets of thick emulsion that have turned brown.
It takes close examination of the paper itself to see that the D-Max dramatically changes with the thickness of the emulsion – the thicker the emulsion, the greater the D-Max (makes sense). So while we coated to a 5mil thickness, if a greater D-Max is required (accompanied by the highlight areas going a bit darker) then perhaps an 8 or 10mil thickness can be tried. By feeling the paper I am guessing that the non-fixable areas are at least 25mil (maybe more), as I can feel a distinct difference.
It’s cool when screwing around can result in actually learning something.