in the application it is being used with the reversal developer it bleaches the image. like any strong fixer will do if you leave a print in it. ( at least that is what I have been told by people with a chemistry background )
It sounds like at some point Rockland may have reformulated their developer from a fairly standard developer (though of the correct strength to give a tintype style image), to a fairly standard monobath and Freestyle never updated their MSDS sheets.
Fixers do have a very small bleaching effect but it is minimal in most cases and only effects the lightest parts of the image or negative where the silver is the thinnest and the silver particles are the smallest. I've only heard it really being a factor in two cases:
- You've got a lot of shadow detail right on the edge of what you can get out of a film and you leave the film in the fixer too long. In this cases the fixer ends up removing that tiny bit of detail you had left there and your shadows end up blocked out.
- Something like a salt print where the silver particles are almost all colloidal (close in size to the wavelengths of visible light). In that case loosing a tiny bit of silver from the already delicate image can be fatal. Salt printers often use pure hypo or rather gentle fixers. Sometimes they just change the ion balance with strong salt solutions which makes the image fade with light but at a hugely slowed rate, all to avoid this change in appearance.
For most other cases you can leave an image in the fixer for hours and still have an image. You may loose a small amount of details in the highlights but the image will still be there.
A couple points.
- A wet plate tintype is very thin silver image by normal standards and even it isn't delicate enough that people really worry about the fixer too much. Just using standard rapid fix for about the right amount of time seems fine.
- A wet plate tintype goes through this weird look as its being fixed where the image goes away and then comes back. I think this is an effect of an index of refraction issue. Regardless the image is never actually bleached out. It just looks that way. I assume gelatin tintypes might do this too (don't know).
- The bleaching action of fixer, does not replace the silver with anything like some other bleaches do. Its more like it's chipping off the edges of the reduced silver grains.
Conventional monobaths all work as a kind of race. A conventional developer consumes the silver halides at the site of a development center (latent image) creating reduced silver grains. At the same time a fixer races to wash all of the unexposed silver halide out of the emulsion, thus fixing it. The trick is getting these two processes in check so that the result is a fixed image. My limited experience with monobaths is you loose substantially on the dynamic range you could get out of the film, but otherwise if you develop at the right temperature these developers do work. This might not even be a down side with a tintype style image as the effect only works over a very narrow dynamic range anyhow (If the silver gets too dense, it starts looking like a conventional negative and you get a mix of negative and positive image effects on the same image).
So could Rockland be relying on the minor bleaching effect of a strong fixer somehow? It doesn't seem very likely. The idea would be to leave the stain of the developer, but not the silver. For starters when Rockland wasn't a monobath this would have never worked without some secondary bleach (the bleaching effect is far too weak on an already formed image). If however they were doing something different in the monobath, any fixer formulated strong enough to remove the silver as it was being reduced would also be strong enough to remove the latent image silver too fast for an image to form, and remove the source material for creating said image. In a sense in order for there to be little to no silver in the final image you'd have to have biased the monobath so far towards the fix side that it destroys the image before it has a chance to form.
It might be the case that the images created with Rockland are composed of a mixture of stain and silver (true of wetplate too when using the pyro developers), and that the percentage of stain to silver varies a bit depending on highlights vs shadows (also true of conventional wetplate under pyro), but I cant see how the bleaching effect of the fixer can be the dominate factor in the image. I don't think you could leave the image in the fixer long enough on a practical level to get rid of the silver.
There was some mention of these images looking slightly green in transparency. I suspect that's the presence of a small number of colloidal particles. These particles being similar in size to red or yellow light tend to reflect this light a bit, and correspondingly look green or blue in transparency because of the excess red-yellow light reflected. Because of this, I don't doubt that the appearance of the image is somewhat effected by the strength of the fixer. I just can construct an understanding where this would be the dominate factor.