Interesting item on NPR the other day on some scientific research that seems relevant to Alt process coating.
The "coffee-ring" effect is that when you spill coffee on your pants you end up with a dark ring at the edge of the stain and a lighter center. In other words the particles in the fluid tend to migrate to the edges of the wet area. However, not all fluids do this. The researcher discovered that fluids containing spherical particles show the effect, while those containing elliptical particles do not - they coat evenly.
This Spring and Summer I've been doing some printing with Gold-toned Vandyke, and had noticed something like the coffee ring - a border of higher dMax around the edge of the coated area. Don't remember seeing this with POP Palladium. So maybe it has to do with the particle shape?
Not sure how this can be useful, but it's interesting to have an possible understanding of what's happening. Also would be nice to persuade the VDB not to migrate to the border of the coating - which I think tends to leave an emulsion-starved area around the edges of a print. Thoughts anyone?