Re: Dichromates ???

Ryuji,

I kind of had an idea that something like that was happening but I'm still
curious, tell me if I got this right? Dichromate as you said is always
active or sensitive to light and heat but it take the presense of those
macromolecules as you say to have a noticable effect such as hardening or
render insoluble those macromolecules.

I suppose then that the dissolved solution is only a mean to put the
dichromate in contact with the macromolecules in a relatively uniform
fashion.

Could there be a point then at which the dichromate crystals themselves or
in solution, would become unusable because of exposure to heat, UV and
whatever else might affect the dichromate?

Would you happen to know the frequency or range of frequencies that
dichromnates are most sensitive to?
I assume this could vary with the various dichromates.

One last question or two if I may, I wonder how the thickness of the
sensitise matrix (say gelatine, pigment and dichromate) on the "tissue"
affect the hole shibang?

How much damage to the negative used to expose the matrix can I expect, how
many prints can I make before I have to put it in the can and is there a way
to protect against damage?

I assume there must be a minimum thickness of the matrix otherwise there
will be an insufficiant amount of pigment to build up the density needed for
good deep blacks or other dark colors . I also assume the penetration of UV
rays inside the matrix is limited to a certain extent and from this point on
any additional thickness will be wasted.

If someone happens to know about this thickness thing it would simplify my
life quite a bit but I assume I'll probably have to do my own testing on
this issue. In the event that I find some interesting results I wonder if
anyone else might be interested.

Thanks a million
Yves Gauvreau, Montreal

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>; <gauvreau-yves@sympatico.ca>
Sent: Wednesday, November 09, 2005 2:46 PM
Subject: Re: Dichromates ???

> Dichromate is sensitive to strong light in all forms but it is
> particularly so when it is mixed with very slightly reducing
> environment, such as gum, gelatin and some other polymers.
>
> Heat can cause similar reactions between those macromolecules and
> dichromate in absence of light. Indeed this occurs at a significantly
> fast rate at room temperature so that once dichromate is mixed in
> those reducing environment the mixture doesn't keep long. This is
> what's often referred to as fog or dark reaction.
>
>
>
>
> From: Stephen Wild <gauvreau-yves@sympatico.ca>
> Subject: Dichromates ???
> Date: Wed, 09 Nov 2005 14:29:33 -0500
>
> > Hi,
> >
> > I've been reading the list for the last few days about dichromate
> > sensitisers used in a few of the alt-process like carbon printing for
> > example.
> >
> > This is probably dum on my part but anyway, here it is: at what point a
> > dichromate solution becomes photosensitive (UV)? I'm just curious, I'm
sure
> > it will work but I can't help myself.
> >
> > I ask this because I just got my potassium dichromate and the container
is
> > not light tight and this mean "UV" could affect the crystalls in some
way
> > because "UV" are present at various levels in practically all (many)
light
> > source. I assume something must happen when the crystals are dissolve in
> > water until the time they get dry for this process to work.
> >
> > I wonder also if other frequencies of the spectrum, radioactivity or
just
> > plain heat could affect the solution. I find it hard to understand why
the
> > dichromates have a tendency to fog (based on many post I saw) if nothing
> > special happens when they are dry, assuming of course the solution is
kept
> > in the dark or "UV dark".
> >
> > I have many more dum questions like this one, I hope you'll forgive me.
> >
> > Thanks for your time
> > Yves Gauvreau, Montreal
> >
> >
Received on Wed Nov 9 15:27:31 2005