Discovery of Flashing

[davidkachel]

Does anyone know who discovered the concept of flashing and when? Need a name and a date, if such exists.
TIA

 

[davidkachel]

Michael,
Why? Do I owe you money?
;-)
Yes, se moi.

 

[Ian Grant]

I think it's a very old technique as it's related to the Herschel effect which is pre/post exposure to a diffrent wave lenght light source that shouldn't fog a film/paaper. Exposure to red safe lights can reduce the contrast of a print where dye sensitisers are used even though the exposure won't fog the material, it's also called latent image bleaching.

My instinct is that Herschel knew about pre-flashing as a method of increasing detail in astro-photography, which is where I first read about it in the 1960's.

Ian

 

[Old-N-Feeble]

I imagine it first began with the invention of the full-length overcoat.

 

[davidkachel]

|-(

 

[Ian Grant]

David, I have a book that should have pre-exposure in and references to very early use but it's rather a large tome and not cross indexed. The term "Flashing" is relatively new because in the 1900's films were so much slower and flash in those days was magnesium powder and dangerous, caused a few deaths

Pre-exposure is an early form of Hyper sensitisation and is the correct term for "Flashing".

The Herschel effect dates to 1839 and Herschel knew then the effects of pre/post exposure to light of different wave lengths.

Ian

 

[ic-racer]

Bowen and Clark wrote it up in 1940. I believe it had been around before then, but not in the formal literature. The effect is not mentioned in the 1911 "Encyclopedia of Photography."

Hypersensitization and Reciprocity Failure of Photographic Plates

 

[cliveh]

I think it's a very old technique as it's related to the Herschel effect which is pre/post exposure to a diffrent wave lenght light source that shouldn't fog a film/paaper. Exposure to red safe lights can reduce the contrast of a print where dye sensitisers are used even though the exposure won't fog the material, it's also called latent image bleaching.

My instinct is that Herschel knew about pre-flashing as a method of increasing detail in astro-photography, which is where I first read about it in the 1960's.

Ian

What has flashing got to do with the Herschel effect? It is not about specific wave lengths of light, but about inertia in base fog to all wave lengths, or those to which the film is sensitive. The flashing effect or pre exposure was probably known by Fox Talbot during his experiments in the 1830's.

 

[davidkachel]

Cliveh,
You are correct. Flashing and the Herschel effect are not related. Don't know how that ended up in here.
I doubt that flashing was known in the 1830's. Fox-Talbot was nowhere near that kind of subtlety then. Neither do I think Herschel would have used it for astronomy unless much later than most of his discoveries. On the other hand, Herschel was capable of just about anything.
I suspect flashing might have come into vogue at the same time as enlarging, where it is most effective, but in reality, I don't have a clue. Haven't found anything.

 

[Bill Burk]

Several early experiments are mentioned in LP Clerc's Photography: Theory and Practice, section 406. Increasing the Speed of Negative Sensitive Materials. C.E. Weinland (1928) is the earliest experiment mentioned.

 

[Alan W]

I imagine it first began with the invention of the full-length overcoat.

First Class!

 

[Gerald C Koch]

I imagine it first began with the invention of the full-length overcoat.

Nice one

 

[Gerald C Koch]

I have the feeling that flashing goes far back in photographic history to a time when it was considered unnecessary, or even ungentlemanly, to claim discoveries. So we may never know the particular person. If it is really important than I would suggest searching the BJ archives.

 

[davidkachel]

BJ archives?

 

[Vaughn]

I have the feeling that flashing goes far back in photographic history to a time when it was considered unnecessary, or even ungentlemanly, to claim discoveries. So we may never know the particular person. If it is really important than I would suggest searching the BJ archives.

I always thought it was the opposite -- a rush to discover light-sensitive processes so that one could get a patent on it for fame and fortune. Thinking of Swan and his patent on carbon printing in 1864.

 

[Ricardo Miranda]

BJ archives?

BJP = British Journal of Photography

 

[Ian Grant]

What has flashing got to do with the Herschel effect? It is not about specific wave lengths of light, but about inertia in base fog to all wave lengths, or those to which the film is sensitive. The flashing effect or pre exposure was probably known by Fox Talbot during his experiments in the 1830's.

Cliveh,
You are correct. Flashing and the Herschel effect are not related. Don't know how that ended up in here.
I doubt that flashing was known in the 1830's. Fox-Talbot was nowhere near that kind of subtlety then. Neither do I think Herschel would have used it for astronomy unless much later than most of his discoveries. On the other hand, Herschel was capable of just about anything.
I suspect flashing might have come into vogue at the same time as enlarging, where it is most effective, but in reality, I don't have a clue. Haven't found anything.

The two effects are very closely related and more importantly Herschell experimented with light of different wavelengths and concluded that what is now termed the "Herschell effect" occurs with exposure to red light and particularly infra-red. The Herschell effect works pre or post exposure, (like flashing) it's the basis of Direct Positive emulsions, although at the time Herschel was interested in post exposure latent image bleaching.

The only differences between flashing and the Herschell effect are that the secondary exposure adds inertia at the wavelengths the emulsion is sensitive too (ie flashing) and the reverse Herschell effect destroys the latent image when that exposure is by Red or Infra-red light.

My point is though that unlike Fox Talbot Herschel took a more scientific approach to photography and experimented with the effects of post exposure of emulsions to various wavelengths of light and at different intensities and exposure times so would have in effect been flashing the materials. He would have been fullyaware of the effects we now term "flashing" but was more interested when the effect reverses and latent image is destroyed and not added to,

Ian

 

[David Allen]

I would strongly suspect that the person who discovered it did so by accident (rather like Solarisation, etc).

Bests,

David.
www.dsallen.de

 

[Ian Grant]

One problem is the term "Flashing" is relatively recent name for the pre/post exposure of films or papers, it was used commercially in printers used in the B&W D & P trade for a number of years to control contrast. Somewhere I have an article or short piece on the use of flashing in the D&P trade. The term isn't in pre-WWII books.

All the early references to pre/post exposure are for increasing the speed of emulsions, rather than contrast control, and it's s technique used primarily in astro-photography. This was Herschel's main field and he discovered the use of Mercury intensifiers to boost negative contrast.

Ian

 

[Lamar]

LOL....

I imagine it first began with the invention of the full-length overcoat.

 

[davidkachel]

Ian,
I think you are confused. The two have nothing whatsoever to do with each other.
Flashing is the application of a sub-latent, uniform fogging exposure that can be applied before or after the main exposure and simply adds density to the lowest density areas of the primary exposure.
The Herschel effect is the destruction of latent image, primarily at the opposite end of the characteristic curve, that reverts metallic silver to silver halide. Also, it cannot possibly be done pre-exposure, because there is not yet any latent image to effect.
I learned a long time ago that anything is possible in photography, so perhaps a pre-exposure of infrared light could have some kind of effect, but I have never seen one described anywhere and if such an effect exists, it would be very unlikely to be the same as post-exposure Herschel.
If you have a reference for a pre-exposure Herschel effect, I would love to see it.

 

[Ian Grant]

Ian,
I think you are confused. The two have nothing whatsoever to do with each other. Flashing is the application of a sub-latent, uniform fogging exposure that can be applied before or after the main exposure and simply adds density to the lowest density areas of the primary exposure.
The Herschel effect is the destruction of latent image, primarily at the opposite end of the characteristic curve, that reverts metallic silver to silver halide. It cannot possibly be done pre-exposure, because there is not yet any latent image to effect.

No confusion at all on my part, the point is that Herschel experimented with different wavelengths of light (not just red & infra red) and different intensities and times, so high intensity and short times and low intensity and much longer times. I've actually said the same as you it's just that both are secondary exposures to light and I've taken a broader view.

I learned a long time ago that anything is possible in photography, so perhaps a pre-exposure of infrared light could have some kind of effect, but I have never seen any described anywhere and if such an effect exists, it would be very unlikely to be the same as post-exposure Herschel.
If you have a reference for a pre-exposure Herschel effect, I would love to see it.

LP Clerc 443 "Various Other Methods" states that a Transparency uniformly fogged by white light can be used to copy a negative which is exposed using red light (generating another negative). The Direct positive films and papers use a variation of this.

The Herschel effect isn't limited to just red or infra red second exposure, gross over exposure to visible light will cause reversal by latent image bleaching, one example is Ansel Adams "Black Sun" in his book The Negative. That's an odd example caused by localised gross over exposure but another is in reversal processing of Black & White or Colour Reversal films where over-exposure at the Secondary exposure stage can cause reversal (latent image bleaching) of what should be a positive image, re-exposure to direct sunlight can cause this

Without trawling through Patents etc I couldn't tell you what wavelength of light is used to pre-expose Direct Positive materials but the secondary exposures are by Daylight or Artificial light. It's possible some emulsions are chemically pre-fogged, the effect is the same.

Ian

 

[Bill Burk]

Hi davidkachel,

You didn't say what you meant by flashing, so now that you clarified, yes. Herschel effect is not relevant to the kind of flashing you are talking about.

It might be a little wrong to say it simply adds density because the paragraphs in LeClerc talk about it not adding density.

And we don't know - are you talking about paper or film? Pre-camera exposure or post-camera exposure, High intensity/short duration or low intensity/long duration...

I think it's fun reading the old research, which goes into such details... and these details may help you find what you are looking for. Many times I find passages in books when I look in the index for "hypersensitization".

 

[Bill Burk]

It's also interesting that I cannot find mention of it in some of my other books by Mees and Todd/Zakia.

So perhaps it is not taken seriously by scientists. Maybe they see it as just a creative application of the additive law of exposure.

 

[Vaughn]

John Sexton described the flashing technique in a Friends of Photography workshop a couple of decades ago. As I understood it, the paper (or film) needs a small amount of light to hit it before any visible change can be seen -- called the threshold of the paper.

If it takes 10 units of light to reach that threshold, then by flashing with 8 units of light brings it up almost to the threshold. If your desired exposure (w/o flashing) thru the negative only allows 5 units of light to hit the highlight areas of the scene where you want some visual tone, then you will remain at pure white with no tone. Flashing with 8 units, then exposing thru the negative will give you 8 units + 5 units of light = 13 units and some tone on the paper. Mid-tones and shadows are receiving many many times that amount of light, so the 8 units of flashing proportionally has no visual effect on them. Normal burning in would increase the density of both highlights and shadows.

Hopefully that is basically correct -- it is what I taught for years. I do not think I would call that hypersensitizing, nor an increase in paper speed (since it is not an over-all increase).