Re: Some points of ponder

There are two things I would like to add to your very thorough explanations:

1) Adding another dye to an already dye sensitized emulsion might turn out
in practice to be difficult.
What about fully exposing and developing the film, applying a rehalogenating
bleach and then re-sensitize in a IR dye bath?

2) Since colloidal silver is said to shift the sensitizing wavelength to the
red and NIR (I think up to 800 nm or so), wouldn't it make sense to slightly
pre-expose the emulsion and subsequently carry out colloidal development?
The colloidal developer might be formed of a very diluted (say 1 : 100)
standard
developer.

Martin

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>; <bsinger@sasktel.net>
Sent: Friday, July 16, 2004 7:44 AM
Subject: Re: Some points of ponder

> 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 02:49:02 2004