Re: Some points of ponder

Boy you ask a simple question ......

Thank you for a very complete and interesting answer. You have
discouraged me, to try this, but now I have a much greater understanding
how it is done.

Barry Singer

Ryuji Suzuki wrote:

>From: bsinger <bsinger@sasktel.net>
>Subject: Re: Some points of ponder
>Date: Thu, 15 Jul 2004 09:32:54 -0600
>
>
>
>>You say you can "dye films yourself". I've never heard of this.
>>Can you point me in the direction of information on how to dye
>>ordinary film to make it more IR sensitive?
>>
>>
>
>Although I discourage you to go this route if the motivation is the
>apparent cost, this may be the only option in some cases. The
>procedure is to make a very dilute solution of infrared dye of
>suitable kind, usually in methanol or other solvent, and immerse the
>film in thie bath for a certain amount of time (typically 1-3 minutes)
>and dry, all in total darkness. This works the best with undyed or
>"color blind" material, but it is reported to work with commercial
>panchromatic films.
>
>Silver iodobromide is practically only sensitive to blue-green and
>this is called "color blind." If the film or plate needs to be
>sensitive to gree, yellow, orange, red or infrared, there needs to be
>something adsorbed onto the silver halide crystal that accepts photon
>of lower energy (such as red light) and inject electron into the
>silver halide crystal in an efficient way. This is called sensitizing
>dye. Dyes like eosin and erythrosin are known as among the earliest
>sensitizing dyes to make dry plates sensitive to green light. Great
>many dyes were subsequently found for the same purpose with better
>performance, different sensitivity pattern, etc. Indeed, silver halide
>photography was the leading engine for dye research as well as gelatin
>research.
>
>Even a same dye can exhibit different spectral sensitivity depending
>on how and how much of the dye is adsorbed on the AgX crystals. One
>extreme is highly aggregated adsorption of dyes utilized in color
>materials (and multicontrast enlarging papers). This type of dye use
>gives very sharp cutoff at the longer wavelength end of the sensitive
>range. But the other extreme of very sparse dye adsorption is
>preferred for infrared plates and films. This makes dying materials
>for IR by immersion very practical. Of course the dye can be added to
>emulsion while emulsion is being chemically digested or at some other
>stages.
>
>Many early dyes were inferior in that their adsorption was poorer,
>especially in panchromatic and infrared dyes. This is why early
>panchromatic plates were very slow and high contrast. Very fine
>grained emulsion was the only practical way to increase surface area
>to enhance dye adsorption. Infrared dye molecules are larger and some
>of the disadvantages remain. If you immerse commercially available
>films in infrared dye bath, I'd try a slow film first.
>
>Classic infrared dyes are dicyanine, kryptocyanine and neocyanine.
>When I wrote him last time, Filip Uhlik had success in immersing Tri-X
>or something in neocyanine solution to sensitize the film to infrared.
>The dye I have experience with is 3,3'-diethylthiatricarbocyanine
>iodide. This type of dye can be systematically "tuned" to different
>wavelengths by changing the length of the bridge (referring to the
>shape of the molecule) and sensitizing property is also perferrable.
>
>I don't know about dicyanine and kryptocyanine, but these dyes can be
>purchased from some specialty research supply houses because these
>dyes are used in laser research today. They typically cost $40 to $100
>per gram.
>
>I skipped a lot of details but I should note that only some dyes are
>suitable for AgX sensitizing purpose. Even if the spectral absorption
>is close to what you need for sensitization, the key is that the dye
>must adsorb well onto the AgX crystals, and must be able to transfer
>electrons (and in some special cases energy) to the AgX
>crystals. (Dyes are not coloring the film base or gelatin binder --
>these can only decrease the sensitivity.)
>
>I would like to repeat -- if the money is the motivation, forget about
>it. But if you want to do IR in 6.5x8.5 or 5x7 negative, there may be
>no other way than DIY approach. (this is my case...)
>
>--
>Ryuji Suzuki
>"You have to realize that junk is not the problem in and of itself.
>Junk is the symptom, not the problem."
>(Bob Dylan 1971; source: No Direction Home by Robert Shelton)
>
>
>
Received on Fri Jul 16 09:14:32 2004