Preparation of glass plates?

[jeffblyth]

Decades ago I used to use the idea of Lin in the original DCG Bell Labs work to stick gelatin to glass. And boy did it stick! Once it stuck so well that as it dried it broke away together with a thin sliver of glass stuck to it!
In the bell labs method a very thin pre-coating of gelatin with dichromate was made followed by a high temperature roasting.

I seem to remember I did a 3% w/w dichromate (ammonium or potassium) with respect to DRY gelatin. And then used this as a 3% gelatin solution to coat one side of glass sheet ( that had been pre-washed either in neat domestic bleach or caustic soda solution) . I then left it in an oven at 200C for about an hour. (Make sure your 200C oven is free of grease laden smoke.)

With respect to the actual diffusion system itself from over 12 years ago I discovered more recently that I could increase the concentration of both silver nitrate and the bromide salt by 50% and get a higher photosensitivity without apparently increasing the final grain growth.
My colleague Colin Davidson’s web site has the original description here:-

http://cabd0.tripod.com/holograms/id3.html
So increase the Ag and Bromide concs stated by 50%
Jeff
PS. You must be scrupulously clean with your very valuable silver nitrate solution. It will so easily get spoilt by organic contaminants and light turning it slightly brown over time. This browness is likely to be colloidal silver and that can cause fog trouble in your plates, ie. they will develop up without light.

[Martin]

You must be scrupulously clean with your very valuable silver nitrate solution. It will so easily get spoilt by organic contaminants and light turning it slightly brown over time. This browness is likely to be colloidal silver and that can cause fog trouble in your plates, ie. they will develop up without light.

Jeff, 19th century photographic literature used to recommend adding a small amount of Kaolin (kaolinite) to the otherwise spoiled silver nitrate solution in order to "decontaminate" it. Would that be a trick worth to be transferred to the 21th century?

[Jeffrey Weil]

Hello Jeff,

I'm glad you brought up the browning of silver nitrate. I got some a while ago from this company

http://www.saltlakemetals.com/Silver_Nitrate.htm

They claim that only unpure silver will go brown and theirs doesn't. I"ve had a bottle, open, for a few years and its still snow white.

I tap some out of the bottle when I use it, I don't place anything into the powder to contaminate it.

Jeff, are their claims true? It looks like it from the condition of my bottle.

Jeff Weil
NorthBeach Holography Inc.

[jeffblyth]

Ag nitrate will keep indefinitely if free of anything that can reduce it to silver Jeff. As a matter of interest, I will mention that if I wanted to make a hologram by the diffusion method in an alkaline polymer that contained a reducing group such as an amine (eg poly dimethyamino methacrylate) then I used to stop bad fogging occurring by adding say 1% acetic acid to the silver nitrate. The brown bottle of silver nitate solution containing 1% acetic acid has kept stable in our lab for 10 years without any browness trace. (BTW the amine groups in gelatin are all neutralized already by acid groups so gelatin is not an alkaline polymer)
Jeff