Odd Gum Bichromate Problem

Colin Graham · Oct 5, 2009

Loris Medici said:
Less won't help I presume; since less hardener = less crosslinking = more swelling, logically... I don't know anything such as "over-hardening"; the excess will evaporate and poison your environment and that's all. (Again, logically.) If there's something particular about glut which I'm obviously ignorant about then disregard this post BTW, maybe the strength of your glut solution is weakened or they've sent you the wrong dilution by mistake!????

Regards,
Loris.

I came across this post (there was a url link here which no longer exists) from PE, which is what made me consider the possibility of over-hardening. It was made in reference to silver gelatin emulsions, so it might not apply to my situation.

But using more glut certainly didn't help- it seemed to progressively thicken even in a 45C bath and get a rich honey color that dried into a dirty yellow on the paper. Which still swelled up and got slimy in development. So less seems worth a try.

Photo Engineer said:
An overdose of hardener put into your emulsion can lead to a coating that is too soft. You have to have not more than 50% of the amount of hardener than can react fully with gelatin. If you go over that amount, it does not harden. Hardener is not washed out unless you process too soon, but in that case the emulsion will probably wash off as well.

PE

Loris Medici · Oct 6, 2009

Ok, thanks much for pointing that out.

FWIW, I personally use Formalin (37% Formaldehyde solution, a pretty old bottle nearing 3 years of storage my shelf now). I add about 1.5ml formalin (since I got the bottle fresh) into 100ml 3% gelatin (200 bloom) and it works like a charm - except for the odor when you size a relatively large batch; I simply close the door and come back to air the room when the coatings have dried... So, I'm with Kerik here.

Loris Medici · Oct 6, 2009

Oops! Missed that one...

Thanks for suggesting. I'm sure it's better somehow but I'm perfectly well with formalin, there's nothing I'd like (or can imagine!) to improve.

Formalin is very accessible to me (cheap and can purchase whenever and wherever I want - our rules are pretty relaxed here in Turkey...), OTOH, glutaraldehyde is a compound subject to special order.

Anyway, will have that on mind if I ever hit to a sizing related problem.

Regards,
Loris.

donbga said:
...

Glut used as a hardener is superior to Formalin or Glyoxal, IME. The hardened paper surface is very smooth and soft and the gelatin cures relatively rapidly (within hours) and resists staining.

You should try some.

Katharine Thayer · Oct 6, 2009

An interesting observation from PE that more hardening=a softer emulsion. Hard to know whether that's a relevant observation or not to our situation here. For what it's worth, I've not seen that with hardening gelatin for sizing.

I have seen overhardening of a colloid with a hardener, once, but that was when I was experimenting with using glyoxal to harden gum for a painting application, and tried several different strengths. The gum with too much glyoxal became very hard and crystalline on the surface when it dried, almost in texture as if it were coated with sugar or something. Again, not sure how relevant that is to the question here, just an observation.

Colin Graham · Oct 6, 2009

Thanks for sharing your thoughts Katharine. I'm probably reaching a bit with the overhardening angle, but it sounded good when I read it.

Anyway, I'm waiting for a paper order so I'll have to stew about it a little longer. I intended to wait to try the glut until after the paper showed up, but I figured what could go wrong?

Loris Medici · Oct 8, 2009

Just for the records; the "overhardening" which I refer to is the phenomenon Colin thinks he is stricken by. (Where presumably more hardener than the ideal will make the sizing soften and cause more swelling...)

OTOH, it's interesting that glyoxal is able to harden gum but formalin isn't. I seems like formalin works with proteins only whereas glyoxal works both with proteins and polysaccharides!??? Anyway...

Katharine Thayer said:
...
I have seen overhardening of a colloid with a hardener, once, but that was when I was experimenting with using glyoxal to harden gum for a painting application, and tried several different strengths. The gum with too much glyoxal became very hard and crystalline on the surface when it dried, almost in texture as if it were coated with sugar or something. Again, not sure how relevant that is to the question here, just an observation...

Colin Graham · Oct 10, 2009

Well, I just can't make this work at any dilution. Dry, the surface seems very rough compared to glyoxal and when the size does manage to survive development the highlights are very badly stained. Once wet, the sizing always swells and gets very slimy. I've asked Photo Formulary for suggestions, I'll keep using glyoxal until I sort it out. Was having relatively excellent results with it, but the worry of yellow stains showing up is always there.

But I gotta ask: you are supposed to dilute the glut concentrate with distilled water, correct? I diluted the 24% 1:10 to make 2.4% so maybe I goofed there..Although I did take a cautious sniff of the 'pure' 24% concentrate, and that's completely odorless, which surprised me after the warnings about the stuff.

Photo Engineer · Oct 10, 2009

Fisheyes, as you call them, and craters as others call them, are repellancy spots generated by incompatible materials being coated one on top of the other. They can be best eliminated by adjusting the surfactant in the coated materials. If you have no surfactant, add one. If you have one, change the level or the type.

Try negatively charged surfactants such as Triton X 200, or neutral ones such as Photo Flo 200. Use very little as the surfactant response is such that it gets you out of trouble at the right level but causes woes when absent or when present at too high a level.

PE

Odd Gum Bichromate Problem

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