archiving silver halide

ron olson · Post by **ron olson** » Tue Mar 01, 2011 1:23 pm

I'm looking to see if there is consensus as to the best way to archive silver halide plates. We're presented with the opportunity to sell a reasonable number of images in the "decorative art" market and I want to see if anyone has suggestions on improving (simplifying?) our tried-and-true technique. At present, and for the last 20 years, we've been applying 2-3 coats of black Krylon spray paint to the emulsion - allowing 15-30 minutes between coats as a function of ambient temperature. Following 24 hours of drying, we then scrape the outer 4-5mm of paint and emulsion (or film) from the edges and attach a second piece of glass using a continuous bead of clear silicone glue. This seems to be reasonably good for archiving but we do occasionally have a plate returned because of humidity damage (fading) and also from color-spotting - a phenomena I cannot really trace in origin but it seems to follow plates hanging in locations where they are subject to hot and cold spells. Any ideas on streamlining and/or improving our process?

holorefugee · Post by **holorefugee** » Tue Mar 01, 2011 2:08 pm

Epoxy is not water proof. It will slow down water coming into the edge of the plate but you would not be able to store a plate at 100% humidity for years. I know of one of your older holograms that has green shifted evenly in San Francisco ambient weather. My two holograms have been rock solid for many years as the humidity is much lower here on average. I have some Triple Take holograms that are gelatin all the way to the edge and have shown no signs of water damage either. I saw Dinesh post that he had some problems with the same method when shipped to India.

A wider seal like 3 mm is better than 1 mm and chosing your epoxy carefully will help a little. If somebody wants to store a hologram under water I don't think there is anything you can do.

Joe has posted a lot about these problems in DCG and some on print out in silver that can be found in the archives.

Martin · Post by **Martin** » Wed Mar 02, 2011 3:21 am

ron olson wrote: Following 24 hours of drying, we then scrape the outer 4-5mm of paint and emulsion (or film) from the edges and attach a second piece of glass using a continuous bead of clear silicone glue. This seems to be reasonably good for archiving but we do occasionally have a plate returned because of humidity damage (fading) and also from color-spotting - a phenomena I cannot really trace in origin but it seems to follow plates hanging in locations where they are subject to hot and cold spells. Any ideas on streamlining and/or improving our process?

Silicone forms a very poor barrier vis-a-vis water vapor. So I'd rather opt for some UV acrylate or epoxy adhesive.

holo_cyware · Post by **holo_cyware** » Sun Mar 06, 2011 11:28 am

Although this has been discussed and rediscussed in the past, there are factors like:

1. The gelatin will still retain some 2-5% water no matter how well dried (even hours in an oven won't remove it). This little water is what attracts more water, rendering the gelatin layer water sensitive.
2. No mater what adhesive you'd use, NONE is water proof. In fact, I don't really think that there is a plastic able to hold the water molecules. The real deal would be sealing the plates by melting the glass edges together. Good luck doing this.

But, there are at least 2 interesting bits that come usefull:

1. Thorough dehydration of the gelatine. This is doable by keeping the hologram for an entire week in an exicator together with some high performance dehydration agent (such as phosphorus pentaoxide or magnesium perchlorate). Jeff Blyth reports this will make a humid proof hologram that will last for years, with no additional protection. This will resist for minutes submerged in water before fading away.

2. Someone recently drew my attention mentioning NINHYDRIN. This is a reagent used by forensics as it has the ability to react with proteins and turning them to something colored (fingerprints for instance). It would supposedly turn the gelatin totally humid proof, and we are talking DCG here.

At any rate, it looks like making a humid proof hologram turns out to be very difficult, especially if for sale to unknown customers and enviroments. We all get used with our own enviroment and we treat the holograms for such conditions.

Jeffrey Weil · Post by **Jeffrey Weil** » Sun Mar 06, 2011 12:12 pm

If its about the 2% of water left in the emulsion attracting more water couldn't you put the plate in a vacuum? That would boil off any water left in the emulsion.

The few seconds it would be out of the vacuum before it was sealed wouldn't be enough time for the water to diffuse back in.

Jeff Weil

holo_cyware · Post by **holo_cyware** » Sun Mar 06, 2011 12:22 pm

Depending on the vacuum...it won't work, probably. My guess is that the water binds to gelatin sort of like it does with certain hydrated crystals (sodium thiosulfate), and it gets difficult to remove.

Martin · Post by **Martin** » Mon Mar 07, 2011 4:00 am

holo_cyware wrote: No mater what adhesive you'd use, NONE is water proof. In fact, I don't really think that there is a plastic able to hold the water molecules. The real deal would be sealing the plates by melting the glass edges together. Good luck doing this.

Some fluorinated plastics (PCTFE etc.) are actually highly efficient water vapor barriers. For example, ACLAR film, which nowadays seems to be widely used for medical/pharmaceutical packaging, comes to my mind. Moreover, there are various laminated films that combine the qualities of several plastic materials into one film structure.

Joe Farina · Post by **Joe Farina** » Mon Mar 07, 2011 7:41 am

In my opinion "archival" is not the best word to use in connection with silver halide holograms, since all bleached silver halide holograms are subject to some printout effects. I'm not saying this is a big factor for the majority of purposes to which silver halide holograms are normally put, but it needs to be taken into account in relation to long-term preservation.

If the objective is to exclude water vapor, then there are quite a few alternatives. As Martin said, silicone is not a good choice for this purpose. Probably the easiest method would be just to use the DCG method for sealing, with a UV-curing optical adhesive such as made by Norland, Summers, or even the hardware-store variety of UV adhesive (which works reasonably well for DCG) called "super glue glass adhesive." Certain types of epoxy can also work well, but the problem with epoxies is that parts A and B need to be mixed, which introduces air bubbles which can be a big problem. (Bubbles are even a problem with one-part UV adhesives.) With DCG, it's also necessary to remove some of the gelatin from the edges of the hologram plate with a razor blade. Silver halide holograms would also benefit from this technique.

The only thing which causes me some concern is that this kind of sealing is not normal practice for silver halide, and I hope it doesn't have a catalyzing or accelerating influence on the printout effect. But I think that's unlikely.

Martin · Post by **Martin** » Mon Mar 07, 2011 8:44 am

Joe Farina wrote:Probably the easiest method would be just to use the DCG method for sealing, with a UV-curing optical adhesive such as made by Norland, Summers, or even the hardware-store variety of UV adhesive (which works reasonably well for DCG) called "super glue glass adhesive." Certain types of epoxy can also work well, but the problem with epoxies is that parts A and B need to be mixed, which introduces air bubbles which can be a big problem. (Bubbles are even a problem with one-part UV adhesives.) With DCG, it's also necessary to remove some of the gelatin from the edges of the hologram plate with a razor blade. Silver halide holograms would also benefit from this technique.

The only thing which causes me some concern is that this kind of sealing is not normal practice for silver halide, and I hope it doesn't have a catalyzing or accelerating influence on the printout effect. But I think that's unlikely.

I've been wondering for a while if a DCG-like sealing wouldn't have a beneficial effect on bleached AgX holograms also regarding printout.
Actually, that's what we did with our Agfa films in the late 80s: with a UV adhesive we used to seal them on glass. Back then that was some acrylate based adhesive produced by Loctite. Not sure, but I believe those holograms all survived until now. In contrast, the holograms we had sealed with drying oils etc., did not.

If you ever expose a wet hologram (bleached with a rehalogenating or a reversal bleach) to a strong light source, you'll notice its greatly acclerated printout sensitivity. That doesn't seem to depend on a particular bleach (I had used EDTA, dichromate, chromate, permanganate, copper, PBU, iodine etc. Bleaches).

Based on that experience, one might speculate that it would be best to seal a bleached hologram under a very dry atmosphere (which might lead to increased dust/static electricity problems). Of course such an environment might also be provided through heating. And one still needs a good water vapor barrier material...

If you want to have extremely good printout resistance, collloidal developed layer would definitely be a serious option. That comes at the expense of high blue (wavelengths) absorption though.

Joe Farina · Post by **Joe Farina** » Mon Mar 07, 2011 9:08 am

Martin wrote:If you want to have extremely good printout resistance, collloidal developed layer would definitely be a serious option.

Yes I agree. I have always been interested in these types of holograms, though I never had one (I would like to). I guess this is really a Russian technique, and I have wanted to ask our Russian friends about the history of colloidal development of holograms (wasn't it pioneered by Usanov?) I would also like to know if the assumed non-printout quality of colloidal holograms has been proven over many years of observation in Russia.