chemicals that become soluble with light

[gattu marrudu]

Hi there,
I am researching for a possible creative solution to an (impossible?) conceptual art project.

I am looking for a chemical compound that acts as a binder, but becomes soluble, or just loses its binding power, by being exposed to light.
My goal is to build some simple structures that break down by means of light, either soaked in liquid or left in open air. I know I could achieve the same result with salt or another soluble medium that melts in water, but I need the light to be the agent that makes this happen.
As far as I know, usually photo-sensitive materials tend to harden with light (i.e. dichromate hardening the gelatin in gum dichromate or similar processes). Does a combination exist that behaves the opposite way?
I know it sounds like a quite wacky question - it is. I would appreciate your help since I have no chemistry degree...

Thanks
gm

 

[Hexavalent]

Gelatin treated with Ferric Chloride and smidgen of tartartic or citric acid becomes quite insoluble. Exposure to UV will render it soluble. This is the basis of the (short-lived) direct positive carbon process.

Novolac resin /diazo is the basis of positive etching resists for printed circuits - exposure to UV renders the resin soluble.


Hope this helps

 

[holmburgers]

I'm not sure if what I'm thinking of is the same as Ian's, but I definitely have read about substances that will do this.

Perhaps it was in Friedman's History of Color Photography in the Carbon & Carbro chapter. I'll see if I can't find it...

 

[gattu marrudu]

That's amazing. Thanks for the tips, I did not know where to start from but I had the feeling that chemicals used in reversal processes would be a good starting point. I will try for sure.
@holmburgers, if you could confirm that reference it would be so helpful.
Thanks a lot!
gm

 

[holmburgers]

gattu, I thumbed through the chapter but couldn't find anything... hmmm... I just can't recall where I read it but I will try to remember.

That book is available online (http://www.archive.org/stream/historyofcolorph00frierich#page/430/mode/2up), though I'm not even 100% sure that's where I came upon this idea.

 

[holmburgers]

Ok, found it. And indeed, it's just what Ian was talking about, but now we have references!

From Friedman's chapter on 'The Transfer Processes':

"Somewhat later, Capstaff modified the procedure. In the original Koda-chrome the non-image portions of the plate were tanned. This meant that printing was to be done from positives, a handicap since it involved another remove from the original. In the newer technique, the image was the silver-bearing portion of the plate. To accomplish this, Capstaff utilized an idea that had already found application in the photomechanical printing trade. Gelatin printing surfaces were prepared by sensitizing a gelatin-coated plate with ferric chloride and tartaric acid. This treatment tanned the gelatin so that it became completely ink-receptive and water-repellant. Upon exposure to light under a negative, the ferric ion became reduced to the ferrous state. This no longer had any specific action on the gelatin (Eng. P. 586/63; cf. also article by J. Joe, Brit. J. Phot., Vol. 60 (1913), p. 250). By this means an imagewise de-tanning of the gelatin took place. Formulas and working directions for the technique are described in the chapter titled: "The Iron Processes" in Wall and Jordan's "Photographic Facts and Formulas.""

Also, I have said Capstaff patent somewhere, which is surprisingly not referenced here. I'll post it once I find it.

edit: Actually, I fear the Capstaff patent isn't all that helpful for your purposes, but here it one that may or may not be the one Friedman is referring to. It discusses detanning by a bleach in the presence of silver, not by UV alone. But it sounds like getting a copy of Wall/Jordan's PF&F might give you a good place to start finding a suitable formula.

Please keep us updated on your project, and some idea of what you have in mind would be welcome too.

 

[gattu marrudu]

Wonderful! I will definitely start trying these formulas out. I am planning to use gelatin as an adhesive to bind an inert, filing material. When the gelatin becomes soluble again, the filler would just detach and fall.
Thank you so much for your advice, I will review your material these days and keep you posted about my progress.
gm