Van Dyke Prints - white marks on paper
I've just started doing Van Dyke prints and have been progressing steadily with one exception. I keep getting these white marks on my prints - see attached photo. I've tried extending the wash times and it hasn't helped. I've tried extending the clearing time and it hasn't helped. I've tried switching out the clearing bath (acetic acid and it hasn't helped). I don't always get the marks - maybe 60% of the time.
Perhaps someone who knows more than me can give me a clue??
Here's my process as it stands right now:
Double coated Stonehenge rising - 20 drops sensetizer plus one drop Potassium dichromate for each layer. 3 hours drying (approx) inbetween coats and before printing.
Exposed under UV for 12 to 25 minutes.
3 clearing baths - 2 liters of water plus 4 teaspoons (approx) acetic acid in each. 1st bath thrown away and replaced every 2nd print. It now becomes
Wash in running water for 10 minutes
Fix - 750 ml water plus 50gm sodium thiosulphate - 2 minutes - at this point I can already see the marks.
Wash for 5 minutes
Tone Rapid selenium toner 500ml water plus 2ml toner - for 2 minutes
Wash for 30 minutes in running water.
Thanks for your help