Sensitizing/Fuming Plates

[Andy Stockton]

Hello All-

I spent the day today on things daguerreian, and ran into an issue at the end of the day that I am hoping to get some help on from experienced folks. Some months ago I fumed a plate over iodine for the first time and the process seemed to be really, really slow. I wrote up the experience on my blog.

The first time I did my fuming in very dim light, as the masters recommend. It made it very difficult to see what was going on. Today I decided to keep the lights on and fume a well polished plate. Here are my lab notes from the exercise:

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LAB NOTES 8/14/2009

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19) OK, I have now fumed my second plate ever and I now see why the first time I fumed a plate that it seemed to take forever! The color change is so faint! I don’t know how I am ever going to see it happen @ 1 foot candle! Under full light 5 seconds of fuming showed faint yellow. The next 5+5+5 seconds progressively deepened the yellow. At 25 total seconds the plate began to show rose patches, and 30 seconds gave me a not fully even rose color over most of the plate.

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So my question to experienced members is this: How do you see the color change in the dim light? Are your eyes just much better than mine or do you use a brighter light than the one footcandle level that I had heard mentioned? Would you be willing to describe how you set up your fuming box and what light source do you use and what physical setup do you have for that light source?

Thanks in advance for any assistance.

[CasedImage]

I guess it is harder to see if you looking directly on the plate, I have a piece of white card taped to the wall of the fumehood and I hold the plate next to that. I use a combination of light directly from the lamp and that reflected by the card. I use a small portable safelight that has a clear 15 watt bulb in it. For the white light I take off the red plastic cover that gives the red safelight. So with the the card I am looking at the white reflection of the card if that makes sense, it may not as this hard to type – earleir today while using the power drill to take the back of on of my buffling paddles I managed drill the phillips head bit through the fingernail of my forefinger. And I’ve been worrying about the handling the 250 ml of bromine I just got! oi vey….

www.CasedImage.com

[drdag]

I compare the plate with an unsenitized one reflecting a crack of light down the side of my garage door 12 feet away. This gets my eyes used to it. It seems that experience and feeling is the best way. I seem to get better at it the more I do. I have made maybe 600 plates and I have about 1 out of 15 failures.

[Mike Robinson]

May I offer a few suggestions.

I sensitize under quite bright fluorescent or daylight (If I’m away from the studio) for First Iodine and Bromine. I look at the surface reflecting a white wall from a very shallow angle. ( say 10 degrees. )

My preferred north light First Iodine coating is an equal balance of rose/yellow

For more even coating I slow the timing significantly by adding 6/16 mesh plain silica gel to the Iodine. My usual coating times to get the the desired colour are 3 to 4 Minutes! I divide the time in half and rotate the plate 180 degrees.

My bromine is also managed with the 6/16 mesh silica gel (a really useful Quickstuff of my own invention – Robinson’s Quick )

Bromine times average in the 60 – 90 second range.

Second Iodine – 2/3s of first under safelight

Slowing things down I believe helps to get greater precision in the coating, which is all important, combined with a perfect polish,

best

Mike Robinson

[jgmotamedi]

Andy, is the Becquerel or traditional?

Not that it matters much, as it has been my experience that the effect of bright lights before the final iodine fuming is negligible. Once upon a time I compared a 15 watt compact florescent bulb about 5 feet away from the plate and an 8 watt (?) tungsten night light, and neither produced a perceptible difference in base fog, using the densitometer function on a scanner to judge. From them on I have used pretty bright lights while inspecting. There was an article by John Hurlock in the Daguerreian Annual about the effects of light between fumings, and as I recall (I read it some time back, so perhaps I remember incorrectly) one take-home-point was that a fair dose of light between the bromine and the final iodine increases plate sensitivity.

[Pobboravsky]

Hi all,

Re: viewing color of iodized plate (Becq): You can safely view the color under normal room light and when you get the desired color, switch off the light and switch on a yellow safelight (like a 15- or 25-watt yellow bug lamp) — then re-iodize the plate for 2-3 seconds. The yellow safelight allows you to see to load the plate into a holder.

Why does this work? While inspecting the color of the coating under bright room light, the light is producing a uniform latent “image” over the entire plate. This latent image consists of sub-microscopic groups of silver atoms. Re-iodizing converts these silver atoms to silver iodide wiping out the latent image.

Another use of re-iodizing: Let’s say a child being daguerreotyped cannot hold still during an exposure, a few seconds re-iodizing allows you to erase the latent image and re-use the plate.

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During I-Br sensitizing the coating can be viewed under bright room light after the first iodizing stage and also after the bromine stage. The last step, second iodizing, is done under safelight conditions. Second iodizing erases the latent image produced during the first two sensitizing steps.

Irv

[photolytic]

Thanks for the credit Andy. I did study the effect of light during fuming in my article “The light after the Bromine” but I fully credited S.M.Barger and W.B.White for first publishing the effect of light during the fuming process on the speed of the Daguerreotype plate in their monumental work “The Daguerreotype Nineteenth-century Technology and Modern Science. Smithsonian Institution Press, Washington DC, 1991.”

As Irving mentioned, the effect of light appears to be due to the formation of free particles or clusters of silver atoms, which Barger refers to as “photolytic silver”, within the silver halide matrix. During mercury development of the plate, these free silver atoms serve as a reservoir of extra silver which can combine with the latent image silver giving the image greater density and increasing the apparent speed of the plate. The formation of photolytic silver by light seems to be confined to the bromine fuming stage. With the exception of hyper-sensitizing or latensification by light, which are essentially pre-development fogging processes to build up image density, extra light during the iodine fuming stage seems to have little effect of the speed of mercury or Becquerel developed plates.

Like the effect of bromine fuming itself, the effect of light during the process increases with increasing light exposure, then plateaus, and eventually declines if a significant portion of the silver bromide is irreversibly converted to silver metal and the bromine gas escapes after excess exposure to light. The more silver bromide initially present on the plate, the brighter the your examination light can be.

The reversibility of this process referred to by Irving was first disclosed by Percy and Shaw in their “Treatise on the Chemical Changes Produced by Solar Radiation” published by S.D. Humphrey, NY, 1852, pp 192-199. They observed that the sensitivity of Daguerreotype plates which had been exposed to light could be restored many times if the plates were exposed to the fumes of both bromine and iodine. While partial sensitivity can restored by more iodine fuming alone, no amount of iodine fuming can restore the lost silver bromide to the coating, hence the need for additional bromine fuming as well.

[CasedImage]

Talas, a bookbinding and conservation supplier in NYC stocks an interesting product that may relate to Mike’s use of Silca gel:

http://apps.webcreate.com/ecom/catalog/product_specific.cfm?ProductID=27849

apparently that talas link doesn’t work, here’s one to a local supplier here

http://www.conservationsupplies.co.nz/lines/548.html

but you can search for it in the talas website under silca gel

www.CasedImage.com

[jdanforth]

I just thought that I’d chime in with my two cents. I sensitize Becquerel plates under red safelight. I check the color periodically using a 25w tungsten bulb and reflecting the plate into a white sheet of paper. I also use Robinson’s Quickstuff in my Iodine for an even coating. I bought it from Talas.

Can’t wait to see some photos from you, Andy!

[Andy Stockton]

Thanks so much to everyone for the wealth of information in your responses. I feel like I have had a personal consultation with most of the heavy hitters in the daguerreian world! I now have multiple approaches to experiment with and will begin to try them on my next “Dag Day”.

To Mike R. and/or Jonathan D. – I had already run across “Robinson Quickstuff” in relationship to bromine and plan to go that way when I finally ramp up for mercury. I had not heard that silica gel could be used as a modulator for iodine to even out the coating.

Would either of you advise me concerning the relative quantities? How much iodine mixed with how much silica gel?

[phuphuphnik]

Am I the only one who doesn’t use quicks? While I don’t enjoy the minute or more exposures, I feel using a quick adds a complexity to the operation that I’m not ready for yet.

[jdanforth]

It’s not so much about speed, phuphuphnik, as it is about making an even Iodine coating. Especially when I work with 8×10 plates it is really tricky to get a nice, even Iodine coating in my makeshift shack of a Daguerreotype studio!

[JWC]

I have a Thomas sodium vapor safelight with standard (orange) b&w filters. Will that be too much light or the wrong color of light for Becquerel daguerreotypes? I also have a Nuarc DLB1012 red safelight with 2 6 watt incandescent bulbs. Would this be a better choice for the second iodine?

[jgmotamedi]

I don’t think either will be bright enough to develop the plates in a reasonable amount of time. Still, it might be an interesting experiment to see what happens if you try the Thomas light.

[Author]

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