In addition:

Historic examples of hand coated gelatin dry plates often show the small drips of emulsion that rolled to the back of the plate as it was tilted to pour off the excess from one end.... and then the shown in the demonstration. These small drips often stuck the back of the plate to the chilling table making the plate difficult to remove. Sliding the plate from the table resulted in another visual artifact that can be used as an identifier.

These particular scenes will also be shown in the next picture set that I upload.