Negatives Appearing positive in reflected light

[htmlguru4242]

I noticed today, while looking at some very thin negatives (from the Tylenol developer), that the images appeared as shimmering positives when held up to an iluminated white ceiling. In additon, if placed base-side down on a black surface and viewed by reflected light, they appear positive.

I know why this occurs, bot it would be interesting to see if this effect can be made useful.

Is there a way to make negatives (on sheet film) that could be viewed as a positive in this way. If I am not mistaken, I believe that this was how collodion negatives & tinypes were viewed, yes?

 

[David A. Goldfarb]

You've discovered the Ambrotype (and a few other similar processes)! These were printed fairly thinly on glass and then displayed in a frame with a black backing, so they appeared as positives.

 

[Donald Qualls]

You have it there, guru -- just underdevelop a good bit, and apply enough extra exposure to get the look you want. Mount over black velvet and you've got youself a direct positive that's (technically) still possible to use as a negative for optical printing (or scan). Get it just right, with the right developer, and the film will look enough like a positive that you'll almost think you have a print...

 

[htmlguru4242]

This could be cool; maybe something to try once I finish my other experiments that are going. Does anyone have a reccomendation for a developer, film, exposure or times?

 

[nihraguk]

I've discovered this phenomenon as well with a frame on my negs that was shot underexposed, and not compensated for in development. Quick question: (i haven't tried it yet) is the neg still printable? All the information is clearly still there... I'm just wondering if the 'positive' image on the neg will present problems during printing.

 

[htmlguru4242]

Well, the image on the negative is not a "positive". It is a thin negative image that appears positive because the blac ksilver relfects light, making it appear white, and the non-silver areas appear dark. The negatives can be printed, so long as they are not too thin, as the image is there ...

 

[colrehogan]

You've discovered the Ambrotype (and a few other similar processes)! These were printed fairly thinly on glass and then displayed in a frame with a black backing, so they appeared as positives.

Kerik showed me some of his ambrotypes and I noticed the same thing at his workshop. I thought it was pretty neat.

 

[gainer]

There was a color process that used a very fine grained plate with a mirror backing. The imaged had in them the interference paterns due to standing waves reflected from the mirror. The colors could be seen by viewing the negative against a black background, IIRC.

 

[Donald Qualls]

Gainer, that was at one time called a "color daguerreotype" or "heliotype". I don't know that anyone has reproduced the process since the turn of the 20th century (separation negatives were SO much simpler, not to mention Autochrome when you could still buy the plates); the original method, as I understand it, was to put a silver chloride emulsion (no information on how they made silver chloride respond to green, much less red light) on glass, then expose through the glass with the emulsion in contact with liquid mercury (the only way to get the mirror layer close enough to the emulsion to get the interference colors). It might be possible, for long term viewing, to vacuum overcoat the (thoroughly dry) emulsion with aluminum, but the requirement for liquid mercury during exposure makes it a hard process to recreate. Even a modern type film product without antihalation would still require a smooth emulsion surface and coupling the reflective surface to that emulsion.

Hmm. I wonder if you could coat the emulsion onto a front-surface mirror? That'd be expensive, though...

 

[Struan Gray]

The process was invented by Gabriel Lippmann . It requires very fine-grain emulsions, since light interference patterns are recorded in the sensitive layer. I don't know of anyone who has revived the full colour process, but Lippmann emulsions are used in holography.

 

[htmlguru4242]

There are instructions for making Lippman Type (panchromatic, super fine grain, very slow) emulsions out there. From what I've read, a Lippman emulsion is very similar to a holographic emulsion. The instrucitons don't seem too difficult or expensive (it's estimated to be about 30cents per 4x5 glass plate).

Front silvered mirrors would work perfectly, as the emulsion and mirror must be perfectly paralell for it to work.

And, to correct Donald Qualls (politely of course), the "color daguerrotpe" that you refer to was called Hillotype, and nobody's yet been able to make an explaination for why it works. Heliotype I believe revers to Neipce's early techniques, I think you were trying to say "helichrome".

The Lippman process, I believe, was attemped by a graduate student somewhere ... though I'm not sure as to how or with what level of success.