How Did They Clean Glass For Commercial Plates?

Photo Engineer · Aug 28, 2010

Guys;

There are two hardness numbers.

1. Bloom index or hardness number expressed in a value from about 70 to 300 which relates to the fraction from which the gelatin is made from the initial mix, and relates to chain length and viscosity.

2. Old style gelatin came in 3 levels of allyl thio urea or "hardness" related to its ability to impart sulfur sensitization to an emulsion. Modern photo grade gelatin is inactive and therefore this term is meaningless. Old text books do not differentiate between these two terms very well.

Make sure you know the difference.

The Bloom index is a measure of hardening capability and rate as well as other factors. The longer you keep a glass plate, the harder it becomes (with formalin or chrome alum or glyoxal or whatever). So, a glass plate frills more or less as a function of age as much as anything else. This is covered in both Haist and Mees but just as hardening in general rather than these specifics.

PE

Ray Rogers · Aug 28, 2010

Yes. Good point.

There are many instances where one has to make an educated guess at which one is being referred to, but in all fairness, Denise was probably looking in glass cleanng/subbing sections where such confusion is less likely.

BTW, I have found a steady change in the reccomended "hardness" over the early years.

Photo Engineer · Aug 28, 2010

Well, in the literature, there was "weak", "middle" and "hard" bloom gelatin referring to Sulfur content, and there was also the same but referring to Bloom Index. It was not until the BI was actually quantified by Bloom that the numbers began to be used, but by then the Sulfur content became irrelevant due to the new refining process for photo grade gelatin.

Early workers used about a 75 BI gelatin but today we generally use a 250 BI gelatin. The 75 hardens very quickly and coats more smoothly (IMHO) than the 250.

PE

wildbillbugman · Aug 28, 2010

Ray,
When I wrote the article on glass cleaning I was using Both gelatin(from the Formulary) and the modified PVA (one at a time! NOT together) I have described in the "Alternative Process" Forum. My statement that"I never have frilling" was absolutely true at the time! It was also true that the method for cleaning glass which I described in the article ALWAYS produced plates which held standing sheets of water without beading. The fact that the latter is no longer true is the reason I started this Thread. I see now that asking questions that people don't know the answer to only creates friction. Go ahead and use glass upon which distilled water beads up. That is only a test I learned from people who coat thousands of square feet of glass per day. Other than that it means nothing.
I also wish to point out that my emulsions today use different hardeners,dyes and emulsification processes than what I did back then. When I wrote the article on glass cleaning, most of my recipes with gelatin came from people with more experience than I had.
Unless someone comes up with some substantial information, this will be my last post on this topic.
Bill

Photo Engineer · Aug 28, 2010

Bill;

I can see your frustration.

Yes, beading is bad and yes a smooth flow of water across the glass is desired. It is important for all vehicles used in coating from gelatin to polymers.

Why this beading changed for you is beyond me. I have no suggestions except that the usual source of this problem is due to oily material in the water used for cleaning, or a change in the "detergent" (read any cleanser into this) used for the cleaning process. At my first workshop at the Formulary, there was a low level oily contaminant in the lab due to other chemicals used there. It caused all sorts of problems. I have found a work around to this problem, but unfortunately it will not work with glass AFAIK.

PE

Kirk Keyes · Aug 29, 2010

Ray Rogers said:
If you remove your false claim that I do not make emulsions,
I will remove my related comments.

Well, Ray, perhaps it's really up to you to disprove Denise's claim. All it takes is a scan or photo of a plate or neg you've made.

I can personally attest to being a witness of plates made by both Denise and Bill. If you like, I can post a photo of some of my (crappy) plates.

Photo Engineer · Aug 29, 2010

Kirk;

I hate to jump into this, but the comment Denise made seems unrelated to the issue and therefore Ray objected to it. I think that we should therefore stay out of it and let them discuss this matter. It is not an issue for me either way.

PE

Kirk Keyes · Aug 29, 2010

PE - OK, one second reading, I agree.

Ray - I withdraw my rude post and appologize for making it.

Kirk Keyes · Aug 30, 2010

As to the earlier suggestion for using hydrofluoric acid, I'd recommend it not be used by people that do not have the safety training that is really needed for using, or the experience of having already used it.

Hydrofluoric acid has serious complications when it contacts the skin or when vapors are breathed. Hydrofluoric acid is an extremely corrosive liquid and is a contact poison. It readily penetrated flesh and destructively binds with bone.

Additionally, I don't think hydrofluoric acid would help. I think if the glass had something already on the surface that was repelling the gelatin, I suspect it would repell the hydrofluoric acid as well. It would probably dissolve a bit of the glass and make a little bit of releif when compared to the unclean surface of the glass.

That said, I once tested the contents of an abandoned 55 gallon barrel to determine what the contents actually were, and it was 50% sufuric acid and 15% hydrofluoric acid. It was for cleaning windows on commerical buildings. Glad I didn't have a job where I had to use that stuff...

Hexavalent · Aug 30, 2010

How about the deadly old-school sulphuric acid + dichromate 'lab glass cleaner'? It is a nasty mixture to work with, but it sure does clean!

Ray Rogers · Aug 30, 2010

Thank you Kirk.
Apology accepted.

(Thanks also to Ron, for his post which resulted in Kirk taking a second look).
---

It appears Hydrofluoric acid may have found use cleaning glass
for some autochrome plates as well....

Given a desire to use chemistry rather than "elbow grease",
I think I would prefer ‘Carey-Lea’.

(The cleaner mentioned by Hexavalent).

Ray

Kirk Keyes · Aug 30, 2010

Hexavalent said:
How about the deadly old-school sulphuric acid + dichromate 'lab glass cleaner'? It is a nasty mixture to work with, but it sure does clean!

That's certainly an excellent glass cleaner - not fast though as you typically place the glass into the dichomate/sufuric solution (aka Chromic Acid cleaner) and let it sit for a while.

Note I suggested the use of NoChromix as a replacement for chromic acid cleaning baths. It's works pretty much as well as chromic acid solution and without the environmentally hazardous hexavalent chrome.

Photo Engineer · Aug 30, 2010

Chromix gives no details in their MSDS citing it as a proprietary mixture.

Wonder what it is?

PE

Kirk Keyes · Sep 1, 2010

Photo Engineer said:
Chromix gives no details in their MSDS citing it as a proprietary mixture.

Wonder what it is?

PE

"NoChromix"

If I remember correctly, it's an oxidizing organic compound. I seem to remember that it does generate some bubbles when mixed up.

How Did They Clean Glass For Commercial Plates?

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