direct positive chemistry

[removed account4]

hi

i was wondering if you photochemistry gurus out there
know of a direct positive developer ?

rockland colloid sells a special developer that is mixed with dektol
for their tintype kits, any idea what sort of curious liquid it might be,
and how easy it might be to home brew ?

many thanks!
john

 

[STEREOKODAK]

Direct Positive

Kodak puts out a Direct Positive Kit for their T-Max film. It's just short of $100 at your local camera outlet. I have checked fairly recently, and it is still available. It is supposed to have everything you need in there.

Of course, you always have DR5 if it's something other than T-Max. They develop direct positive, so maybe they could give you advise.

Randy

 

[AgX]

The term Direct Positive is used differently:

Yielding a positive without copying

-) by a 3or 4 stage process (dev, bleach, fog, dev)

-) by special film that turns into a positive in 1 stage (dev)

-) by DTR

I guess John is wondering about a 4th way...

 

[Ian Grant]

Kodak puts out a Direct Positive Kit for their T-Max film. It's just short of $100 at your local camera outlet. I have checked fairly recently, and it is still available. It is supposed to have everything you need in there.

Of course, you always have DR5 if it's something other than T-Max. They develop direct positive, so maybe they could give you advise.

Randy

That's not what John's asking.

Think about how if you look at the emulsion surface of a negative and watch light reflecting off it suddenly you view a positive.

The developer additive is doing much the same but chemically, it's forming a type of colloidal silver that looks lighter than the background. It's possible a Cadmium or Lead salt would work, there may be a less toxic alternative but my notes are in the UK.

I did try a "white toner" back in the 70's while doing some research for work, that reverses an image, we wanted to coat emulsion on a black surface and get a white image on it. It worked but it was a dirty white

I look tomorrow John, I may have a PDF of one resource here in Turkey.

Ian

 

[removed account4]

thanks for your responses ..

it isn't a bleaching kit like for making black and white transparencies,
or process like dr5 ...

its what ian suggested ... some magical substance you put in the developer
and it lets the silver emulsion look like a positive when on a black background.
i don't know if it has to be used with dektol, or can be used with other developers ...
the favor dektol because it works well with their LSEs.

thanks !

john

 

[holmburgers]

This is fascinating, I've never heard or thought of such a thing.

However, I have noticed that with Delta 3200 negatives the image appears positive when I hold them up against my darkroom curtain. It must have something to do with the thin negatives or something, but IDK; doesn't work with TMAX.

Interesting indeed, looking forward to following this.

 

[greybeard]

its what ian suggested ... some magical substance you put in the developer
and it lets the silver emulsion look like a positive when on a black background.

The "positive" part comes from scattering when you view it against the aforementioned black background; otherwise, it will look like a really, really heavy negative. I believe that the term for what you are looking for is a "physical developer", in the sense that silver (or some other metal) is accreted onto silver nuclei resulting from reduction of light-exposed silver halide. It wouldn't surprise me if some archaic formula for an intensifier would do this.

There is a technique for bringing out latent fingerprints that works similarly. A solution containing complexed silver is applied to the latent print, and silver metal "plates out" where compounds in the fingerprint cause the complex to decompose. A patent search might turn up a candidate formula, but I've never seen a DIY one published.

 

[removed account4]

thanks greybeard

after poking around on their website again, i found the msds stuff
and it suggests there is a weak fixer and weak bleach in the magic-stuff.
from what little i know of photo chemistry, it looks like what happens is,
the image is underdeveloped in a monobath,
then the bleaching agent turns the blacks off white or creamy white or white.
the mid tones stay around the same, so it looks like it is reversed.

not sure if this is what is happening, or if it is something else more high-tech.

i ordered a kit, so maybe i will report back and say what i saw first hand ...
thanks again

john

 

[holmburgers]

I don't believe that this is exactly what you're looking for, but I came across an interesting mention of direct positives in J.S. Friedman's History of Color Photography and thought I'd at least share it. Unfortunately the exact page is not in the Google books version, but it's the last paragraph on page 442 (below) and Google books picks up on page 443 where you can read the continuation, starting with "Several Explanations..." etc.

Last paragraph on pg. 442 says...

This reaction has been utilized to yield direct positives, a procedure described by Hooft in his British Journal of Photography article [Vol. 85, 1938, p. 229]. He sensitized a silver-halide emulsion, specifically a sheet of enlarging paper, with ammonium dichromate and exposed it under a negative. After washing and drying he gave the entire sheet a flash exposure and developed normally in a paper developer. An image indentical with the negative resulted. It appeared that the orignal exposure under the negative created insensitive or desensitized spots, which did not form a latent image when flash-exposed. Hence the developed image corresponded to the original.

"This reaction" that he refers to, well, I'm not exactly clear what reaction he's talking about to be honest; something to do with sensitizing dyes, supersensitization, errr.... etc.

If clarification is requested, I'll be glad to back up and start typing more.. But damn Google books for missing the pages because I can't see the connection between this paragraph and the preceding ones, but I'm sure many others could! Don't shoot the messenger....

Cheers!

 

[Marco B]

Eh... time to have a look at the last post in my "Hippolyte Bayard direct positive process chemistry?" thread perhaps :

(there was a url link here which no longer exists)

Marco

 

[David William White]

John -- once in a while I make a paper or film negative that actually sweeter or more intriguing than its positive. Usually abstracts. I've not gone out of my way to collect them, but I sorta feel that could be up your alley.

 

[holmburgers]

Eh... time to have a look at the last post in my "Hippolyte Bayard direct positive process chemistry?" thread perhaps :

(there was a url link here which no longer exists)

Marco

That is definitely an awesome looking paper... I will try to print it out (when my boss isn't around ) and read it. Very good find!

I'm not sure if I can be of much help, but I'll definitely watch it closely.

Cheers!

 

[Marco B]

That is definitely an awesome looking paper... I will try to print it out (when my boss isn't around ) and read it. Very good find!

Thought so :joyful:, using this description, it must be big fun to try out if you have the basic chemicals at hand, as some of the alt-processes people do, or the ones making their own emulsions...

 

[holmburgers]

Are you referring to the one I posted above, in this thread? I concur! I wonder if potassium dichromate would do the same thing as ammonium, as that's what I've got.

 

[Marco B]

Are you referring to the one I posted above, in this thread? I concur! I wonder if potassium dichromate would do the same thing as ammonium, as that's what I've got.

Ah well, I was referring to the document by Tania Passafiume about Hippolyte Bayard's direct positive process in the other thread I linked. Don't know if you were, can't remember having seen dichromate mentioned there in the very quick review I did, but what the heck... you seem to enjoy all of your experiments, whatever the source!

 

[holmburgers]

Gotcha... I'm on board now.

Yeah, I love this stuff. I'd much rather discuss actual photo chemistry, technique, history, rather than some of the other drivel that gets discussed on APUG. And honestly, I'm still such a newb when it comes to actual darkroom stuff; I've only been at this for about a year and only have a handful of prints to show for it. But the theory behind things... that's the kind of stuff where you can make progress just by closing your eyes and thinking.

So far, most of my experiments (like the slide film screen-plate thing) don't require that I do the processing necessarily. However, having a few chemicals lying around for a few months and you start to realize how wide the uses are for some of them. I.E. K Dichromate.

 

[Marco B]

Yeah, I love this stuff. I'd much rather discuss actual photo chemistry, technique, history, rather than some of the other drivel that gets discussed on APUG.

I fully concur. Up to about 5 years ago, I was completely ignorant of the many historic processes that exist. A B&W picture was just a B&W picture, at the most in a true B&W version, or a brown sepia tone version, of which I had no idea how it became that color, other than "being old" :confused:

Now I know that there is really a host of chemical processes and techniques that may result in a B&W or sepia toned image, not to mention all the other varieties of colors, and that one should be extremely careful when "identifying" a certain historic photo as belonging to a certain process.

APUG really has opened my eyes here, and I often feel like some archaeologist digging up some ancient historic site, when I learn about new details pertaining to the history of photography I hadn't ever heard about, whether it is processes, equipment being used, purposes for which photography is or was used etc...

Really a whole new hidden world turning up

By the way, I don't know if you've already seen it, I linked this very interesting document from the APUG Links section too, and several times in threads, but this document is certainly worth a read if you love the history of processes in photography:

"Photographs from the 19th century: a process identification guide"
by
William E. Leyshon

(there was a url link here which no longer exists)

Marco

 

[holmburgers]

Will the Circle be Unbroken?

That is an epic paper I'll try to go thru it, but indeed it looks rife with information!

I like what you say about archaeologists! I also feel like perhaps there is a drive to learn the history because if the day comes when film is no longer manufactured, the amateurs who can make their own emulsions, developers, etc. will still be able to keep the flame burning and not let nearly 200 years of science die. (note title of post)

Also, when I'm reading these old books from the library and the most recent check-out was 1972 I really feel like I'm doing justice to the researchers who literally devoted their lives to the photographic processes we take for granted today.

** and I promised myself I wouldn't cry! **

 

[Photo Engineer]

I have to add here that there is no process of the sequence Develop, Stop, Fix, wash that will yield a direct positive image from standard film or paper products unless you go through a lengthy chemical pretreatment as noted above. Or, you have to make a special coating to achieve this. You cannot just doctor the developer and get a positive image. As Ian noted, there are special toners and toxic materials that can be added or worked with that can give the appearance of a positive image.

There are direct positive photo products that will give positive images with the simple process sequence above, but these are not readily available. They are made though and are listed in some threads here.

PE

 

[holmburgers]

Hey, I think I figured out a method worth trying.

If you look at post #9 up above, it's going back to that.

I read through it again and it makes sense now, nearly. It capitalizes on the tanning action of dichromate salts (potassium or ammonium). If it is tanned, it is impermeable to a developer solution.

In short, you sensitize an ordinary piece of enlarging paper in a solution of ammonium dichromate, as you might with a carbon tissue. Then you expose it under a positive. This exposure serves to affect the sensitized gelatin in the clear spots of the positive, the highlights. The paper is then washed and dried to remove the dichromate. And now it is flash exposed. This exposure fogs the whole sheet. Then you develop it in an ordinary paper developer. Where the gelatin was tanned (hardened), the highlights are left undeveloped.

Sounds pretty easy!

In the book Friedman points to two possible explanations; one is that the tanned gelatin doesn't allow-in developer solution, and another is "that one product of the photo-chemical reduction of dichromates is free chromic acid, which in this case would immediately destroy the sensitivity centers of the silver halide of a latent image in these areas." He goes on to say that if the latter is the case, a better procedure would be to do the flash exposure first, then sensitize w/ dichromate and expose under the transparency, develop.

So you've got two ways to try it.

Lastly, "alkaline solutions will penetrate even highly tanned gelatin", so the lowest alkalinity developer is preferable.

But I think this could be a cool thing to try out, and it makes sense. Plus it uses only one extra chemical, one that is in many an alt processors cabinet.

Thoughts?

 

[nworth]

AgX accurately described the films and processes. Many, but far from all, black and white films can be reversal processed for direct positive results. The film Kodak recommends is its TMax 100. You can search to find a lot of references for reversal processing in the APUG archives. The first developer is normally a high contrast film developer with a silver solvent added. Kodak D-67 is typical, and it is D-19 with 2 grams per liter of sodium thiocyanate added. The first development is followed (with appropriate rinses and washes after each step) by a non-rehalogenating bleach (like Kodak R-9, a dichromate bleach), clearing bath (sulfite solution) re-exposure or fogging bath, second developer (usually something like D-19 or Dektol), fix, and wash. Black and white reversal kits are available, but it is much cheaper to mix your own, especially if you intend to do a fair amount of work.

 

[holmburgers]

nworth, if you read on you'll see that the OP is not asking about reversal processing per se, but "direct positive" chemistry. Semantically similar, but historically two different ideas.

 

[removed account4]

i finally figured out what the magical substance was ..
... fixer and a bleach ...

thanks everyone for helping me figure out
the " riddle of the magic-substance " ...