AZO?

[maxbloom]

Okay, so I know that Azo is a silver chloride paper. Everyone is always talking about the joys and capabilities of silver chloride papers. But what's the significance of the name? Surely there's some azo compound in the paper? What is it? Is it in any way chemically similar to the azo dyes I read about in other photographic papers like ciba/ilfochrome? In general, are Azo papers (Kodak and non-Kodak) unique because of some combination of silver chloride and azo compounds, that might separate them from non azo containing silver chloride papers? Sorry, lots of technical questions I know.

 

[Curt]

No, I just won't do it, I'm tempted but I just can't.

 

[maxbloom]

Am I that stupid?

 

[maxbloom]

Let me guess. They call it Azo because of Amidol?

 

[PHOTOTONE]

There are no Azo chemicals in Azo paper. Azo is a trade name for a particular Silver Chloride contact paper which used to be made by Kodak. At one time, most paper manufacturers had a similar paper. Velox is another paper that was made by Kodak that was similar. Many paper names are just trade names.
Azo has developed a legendary following since its demise. This is partially due to the quality of the images, and partially due to the fact that no one is making a similar paper.

 

[maxbloom]

Right, but you didn't answer my question. Why would they call the paper Azo if there are no azo compounds in the paper? Is it because it used to only be developed in amidol or something?

 

[TheFlyingCamera]

Like any other silver paper, you can develop Azo in just about anything you want to. There are just a few highly visible practitioners of the Azo/Amidol pairing, and so people think the two are a requirement.

 

[maxbloom]

I understand that, but it still doesn't answer my question...

 

[ann]

Perhaps PE will chime in here with some back story about this name; however, how does anything acquire a name.

Sometimes it may have something to do with it's make up or just a marketing whim.

Years ago my favorite paper was Brovia, heaven only knows why it was called that and frankly it never crossed my mind to wonder about it's name, altho i still miss it's wonderful blacks.

 

[maxbloom]

FYI It was called brovira because it was a bromide paper. I'm hoping that PE will, indeed, chime in at some point.

This is along the same lines of why I'm wondering about the name Azo for a paper that apparently doesn't have any azo in it! :confused:

 

[removed account4]

max

i think it was just a name.
like dektol is a name, metol ( or kodak's name for their metol was elon )
or selectol o r... i think azo was just a name, nothing more than that.
like kodak is just a name, cause it sounded good, and was easy to remember.

i could be wrong though...

 

[maxbloom]

It is catchy. I'd love to believe that's the case but I just don't believe they would use the name of an organic functional group without it having any relevance to the paper.

 

[ann]

i know that Brovira has a high level of bromide but it was also full of cadmium so why not call it caovira.

 

[maxbloom]

i know that Brovira has a high level of bromide but it was also full of cadmium so why not call it caovira.

Because cadmium was a staple of most papers for a long time. Would be like naming a paper silvira.

 

[ann]

and bromide is in a lot of papers, but i surrender at this time.

 

[Photo Engineer]

Velox, Velite and Azo were Kodak's trade names for slow gaslight or UV sensitive products that could be used under low room illumination. Azo had the best tone by far. Some early papers were stabilzed by using Sodium Azide which is explosive and hard to handle. Maybe this is where it came from. IDK.

A derivative of Sodium Azide is used today in airbags in cars to puff them up when struck hard.

Agfa produced a similar paper to Azo called Lupex. Azo and Lupex were both Chloro Iodide papers. That is, they were made with both chloride and iodide. I have argued this point before here, but it is true.

Some eastern European companies still use Sodium Azide for stabilization of emulsions. See Jim Browning's web page for a formula which uses it.

Kodabromide and Brovira were both Silver Chloro Bromide emulsions with a dash of iodide, a big slug of cadmium, some formulas had mercury and lead. They were a toxic brew depending on contrast grade and image tone. Cadmium was not used in Azo AFAIK.

Cadmium was used in the make or just before coating and was used at about 5 - 15 grams for every 108 grams of silver which was a BIG dose. Current chemicals that replace Cadmium are used at about 6 x 10^-6 grams / 108 grams of silver, so even if they are a bit on the toxic side, they are used at levels of 10,000,000 x lower or thereabouts.

Does this help?

PE

 

[htmlguru4242]

On the topic of Azo and what it contains,

PE, just out of interest, do you have any [relatively] specific information about Azo as to what it contained / how it was made?

 

[blaze-on]

Is there tri-x compound in tri-x film? or was it used for filming XXX movies?

 

[Photo Engineer]

Azo was a single run silver chloro iodide. It was a very simple emulsion similar to the one I posted here by Bruce Kahn, formerly at RIT. It contained a stabilzer such as Tetra aza indene, and a sensitzing dye (IIRC - it may not have). It had no Cadmium in it AFAIK, but Kodabromide and other enlarging papers did.

After the run, it had a very short digestion period and then was coated with muchochloric acid and formaldehyde hardeners. It had an overcoat applied at a second coating station. At one time, it used saponin as spreading agent, but Kodak was changing over, so I don't know if that was used in the later batches.

The Agfa version used sodium sulfite and formalin only with a sulfonic acid spreading agent (again IIRC).

Kodak Azo was coated on a tinted SW baryta support. At one time, Azo was supplied in 19 different paper surfaces. Samples are in the GEH archives and viewable by appointment.

There was once a warm tone Azo which contained ammonium salts during the run, and also copper salts. This was similar to the Agfa Lupex.

PE

 

[Vaughn]

Thanks, PE. Your willingness (and patience) to share info is much appreciated!

Vaughn

 

[jgjbowen]

Does PE stand for Photo Engineer or Photo Encyclopedia? You never cease to amaze me....

Thanks for all you share with this community!

 

[htmlguru4242]

Interesting to know, PE - I didn't realize it was so simple. Did the emulsion remain basically the same from its introduction right up until its demise?

 

[Curt]

Are there any Rodents in Rodinal?

If PE doesn't know, it isn't worth knowing.

 

[TheFlyingCamera]

if not rodents, then perhaps rhododendrons oh, wait, that would be rhodinal

 

[Photo Engineer]

Azo and all of the other emulsions varied quite a bit from their very first incarnations. They evolved over the years as gelatin changed, support changed and etc.

For example, one product could not be made with the same image tone when Cadmium was removed. It therefore had to be discontinued. I forget the product, but it was either Opal, Medalist or one of those era emulsions.

A major change in all papers took place when the active gelatins were no longer used. All papers were reformulated to use sodium thiosulfate at about 100 mg/mole of silver (108 grams). Silver Chlorides were one of the most difficult to convert and were the last to use active gelatins. In fact, sulfur + gold sensitization on AgCl was active as a big project when I joined Kodak, as it was desirable to make a high speed fine grained print film for motion picture. A few papers could not be reformulated properly for use with inert gelatins and this led to their being discontinued.

Ektacolor 20 was discontinued due to Cadmium at about 15 grams / mole and a Mercury salt at about 0.1 gram / mole. It was reformulated with organic compounds to give the same curve, higher speed and fixed speed from batch to batch with 2x the development rate. This was not applied to B&W papers as they could not adjust the already short development times for the single layer materials, but eventually it evolved into the modern papers which develop to completion.

Azo remained virtually the simplest formula Kodak produced, but papers such as Kodabromide were quite complex by comparison.

For the Ilford, Agfa and Fuji guys reading this (and some of my other posts - or maybe even some of the Kodak guys), I'm drastically simplifying things and also not disclosing everything to avoid disclosure of confidential data in public.

Oh, there are no rodents in Rodinol. But, there are some rodents living under my front porch. I've tried alum and it chased them off for a while but they finally decided that they could stand the pucker power of alum and dug through it again today twice. I may try HQ to see what develops.

PE