Direct Positive Paper - How Does It Work?

[holmburgers]

Well.... I'm not in school at the moment, but I like to think I'm a good student.

Not a suckup though..... just genuinely interested. Why do you ask, praytell!??

 

[Ray Rogers]

You ask such easy questions!

 

[holmburgers]

Whatchyou talking abou Willis!? I can't tell if there's sarcasm involved or not. Heck, I though it was a doozy of a question.

Perhaps you are referring to the question "Could that be elaborated upon?", which indeed has an easy answer... yes. Perhaps I should've said, "will someone please elaborate!"?

 

[Ray Rogers]

No, Its a doozy!

 

[holmburgers]

Haha, ok... wakarimasu!

I really don't understand how a silver-halide can be so exposed that it effectively becomes "unexposed". And does that only exhibit itself upon chemical development? What's more mind-boggling is printing-out solarisation... can that happen?

 

[Ray Rogers]

I think PEs got his work cut out for him with that question.
I haven't seen that much "punch" packed into such a few number of words in a long time.
Good One.

 

[holmburgers]

Here's what DA Spencer says, courtesy of wikipedia... Due to halogen ions released within the halide grain by exposure diffusing to the grain surface in amounts sufficient to destroy the latent image

And to clarify, this is totally different than "artistic" or pseudo-solarization done in the darkroom, practiced by Man Ray and others.

 

[Ray Rogers]

Haha, ok... wakarimasu!

I really don't understand how a silver-halide can be so exposed that it effectively becomes "unexposed". And does that only exhibit itself upon chemical development? What's more mind-boggling is printing-out solarisation... can that happen?

Did you know that it can happen more than once in the same emulsion?

I would have to look up the details that I have collected on it over the years, but I think you will find that there are compeating reactions going on all the time... literally all the time, and under certain conditions, the "other" side wins.

Hopefully PE won't laugh too hard at my comments, nor Keith the Physics Guy for that matter!

Actually... I THOUGHT I had read about pinhole solarization...
or was that just my imagination entertaining me?

Print out solarization hum I think so, but don't remember (Yawn)

I have seen Polaroid (Fuji FP100 actually) solarize, but that doesn't count, does it?

 

[Ray Rogers]

Here's what DA Spencer says, courtesy of wikipedia... Due to halogen ions released within the halide grain by exposure diffusing to the grain surface in amounts sufficient to destroy the latent image

Yes, but (as quoted above anyway)
wouldn't that leave you with simply an unexposed image;
that is, no image rather than reversal?
I think there must be more to the story.

I think I am going to sleep on it.

Good night.

 

[Photo Engineer]

Well, to cover all of these in one ansewr, Solarization does not require layered emulsions so the initial premise posed by Ray asking about the layers involved is not relevant. Solarization can take place without layers in the grain.

Spence is right. You have to remember that Solarization is taking place imagewise and therefore you have a positive and a negative image superimposed. Done right, the meeting place has low enough fog that you see both a negative and a positive image, but the image is not a super image. It is marred by many imaging artifacts caused by both the negative and positive superposed images. A reversal emulsion made intentionally for a direct positive image separates the two images by correct crystal structure and chemical means so that you see one, or the other, but not both. So, there are two types of reversal here. One is "bad" (Solarization) except for artistic effect and the other is good and is engineered into the product.

Remember though that all normal emulsions can be Solarized by the method of overexposure and as described by Spence. We normally repress that possibility by chemical means so that it is not normally seen.

PE

 

[Ray Rogers]

Sorry,

but I posed no initial premise about solarization needing layers.

My question was only about DR emulsions, which, IIRC,
has functionally different "regions".
Chris simply asked about solarization in general, afterwards.

My question seems to have gotten lost in the shuffle (shuffel?)
so I will reword it and bring it to the top of the shelf, so to speak.

PE wrote:
If they overlap by a great deal, you see it as fog[/I]

Ray responds:
What can be done to reduce such an overlap ?

 

[Photo Engineer]

Solarization does not need layers. Direct reversal often does.

As to the methods used to reduce overlap, sorry, but I am not an expert in this area and cannot say for sure. I can make an educated guess that it is due to 2 factors with Reversal F. One is the thickness of the two layers and the thickness of the transition between them. The second is the stress level (fogging) impressed on the core of the emulsion, along with the two chemical sensitization layers imposed on the emulsions two "layers".

Now, as this is way way way beyond the scope of what we are intending to do here, and way beyond what I have worked with, I don't think that we can carry this any further. This is one of those deep dark secrets that only the initiated can join into, and to do that, I believe that there is a rather steep initiation fee. Probably involving sending an arm or a leg!

JK..

PE

 

[Hexavalent]

I believe that there is a rather steep initiation fee. Probably involving sending an arm or a leg!

JK..

PE

Is it okay if I send the arm or leg of a third party?

JK

 

[Ray Rogers]

I'm sure that day will come...



There is one other point that really should be mentioned...
before we return to the future passed...

you wrote:

If you don't do it right, the negative and positive images "leak" between the "layers" and you see low discrimination!

&

It is the job of the photo engineer to separate these two phenomena in speed so that they don't overlap. If they overlap by a great deal, you see it as fog

This SOUNDS like it can be done so correctly, that there is no problem,
but I am under the impression all DR materials suffer from this problem to some extent (high fog), compared to either negative or positive emulsions

Is this correct?

 

[Photo Engineer]

Is it okay if I send the arm or leg of a third party?

JK

Absolutely!!!! Can I make some suggestions?

Ray;

In my experience with DR emulsions from the product development side (not from the emulsion side), I have never seen a "perfect" DR emulsion with both low fog and good separation. Either one was bad, or the other was bad, or both were bad! At least in comparison to the desired aim. Usually, we had to accept a tad higher Dmin with good separation of the neg-pos images as the best of any of the possible results. Even so, some very bright highlights showed a dark spot in the center. This was the "fried egg" effect as we called it.

PE

 

[Ray Rogers]

Is it okay if I send the arm or leg of a third party?

JK

Absolutely!!!! Can I make some suggestions?

Ray....

Just coincidence?

 

[richard ide]

At one time, Agfa sold a film which would yield what looked like a high contrast line drawing of the subject. The film acted both as a negative and positive emulsion. If you photographed a step wedge, both ends would be clear with the middle tone(s) as black. You could shift the position of the developed area with exposure adjustment and the width of the band with development.. IIRC a special developer was used.

Ron,
I made contact prints of drawings etc with autopositive materials made by Kodak, Fuji, Dupont and Agfa. Some were exposed through a yellow filter to give a positive image (5000w UV light source); but could also be then exposed to white light to produce a normal negative image in addition.

Positve drawing + yellow filter = positive image on photographic medium.
2nd exposure - negative + white light = additional positive image on same medium.

Do you know how this type of emulsion worked?

 

[Ray Rogers]

The first paper you described was quite amazing stuff!
You could do some really schizophrenic color work with it.
I have technical data for it, but it really is pretty special stuff.

Did you use it yourself?

 

[Photo Engineer]

Richard;

I am not really familiar with the product. It was a "rare bird". Sorry.

Ray;

If the shoe fits...............


PE

 

[holmburgers]

I've seen that Agfa film (online that is...); Agfacontour I believe.

Here are some examples of one, Josef Šechtl, and his work with it... http://sechtl-vosecek.ucw.cz/en/expozice2.html

I'm still left wondering about normal paper/film solarization...

 

[richard ide]

Thank you Ron. Some of the reprographic materials were a little out of the ordinary; but must have been a huge source of income for Kodak and the others.

 

[Ray Rogers]

I'm still left wondering about normal paper/film solarization...

Maybe there's a little trouble in Paridise dismembering the problem?

If I am still here tomorrow I'll try and lookit up.

 

[Photo Engineer]

Please look at Mees (revised edition), Chapter 7. He gives a complete description of Solarization as well as a discussion on core shell sensitivity. I really don't intend to scan in the entire chapter and all of the graphs of sensitometric curves. I suggest that this is good reading for you Ray and you Chris. There is deeper and more modern theory, but I just do not remember it.

PE

 

[holmburgers]

That works for me Ron... I love a good trip to the library!

 

[Ray Rogers]

There are several issues in trying to answer Chris's question.

The first is that it is often hard (at least for the non specialist)
to recogonize the difference between known facts and theory,
and between discarded or discredited theories and
the modern or currently accepted theory.
Often books present knowledge as a collection of evolving theories.
I often find this frustrating and long for a Detective Friday
who would bring us 'just the facts'.

We also have to consider that Kodak and other industrial research giants might have actually grasped certain theories or aspects to a deeper level than the rest of the world's scientific community.

Anyhow a good trip to the library should be helpful in anycase.