White small spots on Cyanotype

[mug]

I'am testing some papers for Cyanotype. Cheap drawing paper gives even coat but low density blue. Some expensive watercolor papers have strong blue, but did not coat even. I get small white spots. What did I do wrong ?
Should I ad some dishwater soap (agapon etc) ? Or an double coating. Or just ad an layer before the coating from harded gelatine ?

 

[ced]

Try wetting agent, also have a bash at double coat.
What do you use to coat brush/rod/foam?

 

[mug]

First I used an hake brush. but yesterday I found an glass rod. For my the rod works very fine, better then expected.
Thanks for your advice. This evening I try with wetting agent.
Dit same watercolor paper with precoat from gelatine. That pre-coat worked very fine with smooth final coat.
But pre-coat cost me day extra (solve gelatine at 40 ºC, coat, dry, harder, dry).
So if I can find an paper I like that's works fine right out of the box, that would be my preference.

 

[pdeeh]

You might want to try acidifying the paper - give it a bath in dilute acid (something like 5% citric acid) then wash and dry before sizing.
Many if not most watercolour papers contain calcium carbonate or similar (acid paper is archivally unstable) but cyanotype dislikes alkalis.
I'm not saying that this will solve the problem, but many things can go wrong or cause problems with alt processes and this is just one. So worth investigating.

 

[pdeeh]

Can I also suggest you give a very full description of what you are actually doing, otherwise we are all working in the dark.
So what papers are you using? How are you preparing them? What gelatine are you using and how are you preparing it and applying it? How are you hardening it? How do you wash your paper after exposure? Are you bleaching or toning? Which recipe of cyanotype sensitiser are you using? How much do you use?

And so on.

Without that kind of information, a question like "why am I getting white spots?" can only be greeted with speculative answers.

 

[Andrew Patteson]

Is the example image coated with the brush? Maybe you were overbrushing and abrading the paper surface?

 

[ced]

For me if I had to start sizing using gelatine for cyano's I would give it up as the expense in extra time takes away the pleasure & simplicity f the process.
If you need/want to size use 1:2 PVA glue to water or arrowroot. The best is find a cheap paper that works well & stick with that.
Have fun anyhow!

 

[mug]

I used Winsor & Newton Artists' water colour paper CP/Not, unprepared right out of the block.
And I use an glass rod to put cyanotype (standard) chemicals on the paper.
Yesterday I tried what member 'ced' advised. Use some wetting agent.
And this works indeed good. Used old Agfa Agapon 2 drops on 6 mL cyanotype chemicals.
So problem solved ! Thanks.
Also did experiment with toning a Cyanotype. I compare strong Thee, strong Coffee and Tannine (from wine making shop). First I bleach with ammonia ~5%
Clear winner for my was the Tannine (50g/L). Thee and and coffee were too soft.

 

[ced]

Tannic Acid 15grm./1 litr. is also very good for toning, using crystal soda 2 tbl. spns./1 litr. as a bleach also works for bleaching.
Glad the wetting agent helped.