Cyanotype - bubbles

[mvons]

Hello all,
I'm working with cyanotype now. I'm trying to do cyanotype on glass. While everything is working and gelatine react to UV. Then I have problem with bubbles that appearing during drying the plates.
They are not visible when gelatine is wet.
Do you know what is the problem and how to avoid that?

 

[koraks]

Could you describe the full process you're going through? At which stage in the process do the bubbles/blisters occur?

Is it correct that you have incorporated the cyanotype sensitizer in the gelatin? What happens if you coat the glass with just gelatin, without cyanotype?

Many more details, please!

 

[mvons]

Could you describe the full process you're going through? At which stage in the process do the bubbles/blisters occur?

Is it correct that you have incorporated the cyanotype sensitizer in the gelatin? What happens if you coat the glass with just gelatin, without cyanotype?

Many more details, please!

I'm following this recipe.
Like I said. I mix all ingredients. Let the gelatine cool down for one night. Then I heat up gelatine and cover glass with this solution.
When wet, gelo looks crystal clear, no bubbles. But when drying they appears.
I didn't check how gelatine without cyanotype chemical will react. I'll check it as well.

 

[koraks]

Ok, see how it works out with the gelatine without the sensitizer. If that dries without any bubbles, I would also be tempted to test a few plates with just the gelatin and the oxalic acid. If that works OK, test a batch with gelatin, oxalic acid and ferricyanide and a separate batch with gelatin, oxalic acid and citrate. By this time you will know exactly when/where the problem occurs, which should help nail it down. If I were to put any money on this, I would say it's either the oxalic acid that foams in combination with the gelatin, or it's just the gelatin by itself possibly due to bacteria or yeast (so fermentation, in effect). But I'd start by establishing trying to isolate specific factors.

How do you clean your glass plates, BTW? When coating with gelatin for other purposes than cyanotype, I usually just do it the way they do it for wet plate collodion: wash with soap, then scrub/polish with a paste of water + calcium carbonate, then rinse that off (you need to wipe it a bit under a running faucet to get the thin veil of carbonate off entirely). This yields a perfectly clean plate to which stuff like gelatin, but also collodion, gum arabic and albumen will stick well.

After cleaning the glass, do you sub it with a thin layer of e.g. gum arabic or albumen? Just running the glass through a 1% solution of either and then letting it run off works well. Heavier layers of gelatin will adhere to the glass much better this way than without any subbing. However, this mostly helps combating issues like frilling along the edges; your problem seems to be a different one.

PS: there's a typo in the recipe you use. It should be ferricyanide, not ferrocyanide. Ferrocyanide also exists, but doesn't work to the best of my knowledge!

 

[nmp]

It's possible that you are not seeing the bubbles in the wet stage because optically they may be hard to discern, but when dried they show up because they have greater refractive mismatch with gelatin in solid state.

If they are indeed forming during drying, it may also be due to less than ideal cleaning of the plate. Normally if the plate is hydrophobic all over, you would just get delamination of the coating. But when there are spots of hydrophobic contamination or the amount of contamination is low enough that the coating does not simply lose the adhesion globally. Instead, since it must relieve the strain somehow, it ends up creating these bubbles - kind of micro-fractures, near the surface. If this hypothesis (that's all this is) is correct, then more meticulous cleaning, kind of like sugested by koraks, might work to alleviate the problem.

:Niranjan.

 

[mvons]

It's possible that you are not seeing the bubbles in the wet stage because optically they may be hard to discern, but when dried they show up because they have greater refractive mismatch with gelatin in solid state.

If they are indeed forming during drying, it may also be due to less than ideal cleaning of the plate. Normally if the plate is hydrophobic all over, you would just get delamination of the coating. But when there are spots of hydrophobic contamination or the amount of contamination is low enough that the coating does not simply lose the adhesion globally. Instead, since it must relieve the strain somehow, it ends up creating these bubbles - kind of micro-fractures, near the surface. If this hypothesis (that's all this is) is correct, then more meticulous cleaning, kind of like sugested by koraks, might work to alleviate the problem.

:Niranjan.

I believe that I cleaned glass correctly. I used soap, then scratch with tape knife and before coating I used isopropyl alcohol.
I will do some tests only with gelatine and oxalic acid.
Will see.

 

[koraks]

I used soap, then scratch with tape knife and before coating I used isopropyl alcohol.

I don't know what 'scratching with a tape knife' is, but I'd really and very strongly suggest cleaning routine as I outlined before, if only because it's proven to work well for over a century. Anyway, I think the other experiments are worthwhile even more, so keep us updated on how that goes.