This image has white marks all over the sitter. I am guessing it is because I took the image at the end of a long shoot and should have changed the chemistry, the image I took right after was fine. So it is a bit of mystery the exact cause, as is proving to be the case regarding wet plate photography with all it’s pitfalls and variables. I recommend changing the developer and the fixer after several plates as (particularly the developer) tends to become a little polluted by the heady mixture of collodion and silver nitrate.
This Is Not Digital 
Are you re-using the developer after each plate! Do you not pour a small amount across plate? Or do you actually bathe the plate in developer? I was taught to use minimum developer possible in one quick fast pour on to plate.
Hi, when I did the course to learn this process, we bathed the glassplates in the developer in a standard developing tray, however I would be interested in trying your suggestion and seeing if I have a better outcome. Thank you for this advice, anything to save chemistry 🙂