From: Amy Cutting (amos1979@attbi.com)
Date: 02/26/03-10:25:05 PM Z
Ryuji,
Just checking to see if you'd received the silver gelatin book yet. I love
mine and am about to dig back into it and figure out a good way to make a
peelable negative off glass (never know what you might need to stick those
things too). Hmmmm. Amy
----- Original Message -----
From: "Ryuji Suzuki" <RSuzuki@MIT.EDU>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, February 22, 2003 3:37 AM
Subject: Re: Glass plates setting temp and health points... (rather
long/2short)
> From: John Glen <microcrystals2002@yahoo.com>
> Subject: Re: Glass plates setting temp and health points... (rather
long/2short)
> Date: Sat, 22 Feb 2003 04:18:52 -0800 (PST)
>
> > What are you talking about here?
> >
> > Maybe I am miss reading something, but what is it with
> > this NOT "gelated" at a low temperature." typically,
> > Gelatin will "gelate" (gel or set) at room
> > temperature, or upon slight cooling.
>
> Gelatin in dispersion form at typical coating temperature is in sol
> form. Sol form and gel form differ in physical arrangement of gelatine
> constituents. Gel form is more regular and gives much better physical
> strength, as well as better hardening response when hardener is
> used. Sol form is softer and does not respond to hardener as nicely.
>
> In order to get the gelain to become gel form (gelation) you need to
> bring the material to a temperature lower than a gelating temperature,
> which is determined by viscosity, Bloom, etc.
>
> Above this temperature, coated material will dry without adequate
> gelating. Physical strength will be inferior, though it may be enough
> if you handle very carefully. It is for this reason I'm considering to
> have a refrigerator - to gel the emulsion before drying. Gel and sol
> are not necessarily black and white. If you dry at a marginal
> temperature, you may get intermediate result.
>
> Thus gelation is not synonymous to setting or drying.
>
> > Commercially, with large amounts to coat, the coating
> > speed is rather fast and cooling (quick setting) is
> > essential... in such cases the exact temperature mmay
> > indeed affect dry "Scratch Strength" or what have you,
> > but IMHO the small scale experimenter has nothing to
> > fear... the results will be OK.
>
> One partial reason modern films are said to be "harder" is because
> coating is done at higher viscosity and gelated at a lower temperature
> than old films. I'm simply trying to get the benefit of good gelation.
> (Of course, modern films use hardener to allow processing at higher
> temperature, but hardener itself doesn't make emulsion hard when it's
> dry. Note again hardener does not significantly influence the
> mechanical strength of gelatin layer when it is dry.)
>
> > In any case the gelatin solution will "gel" without a
> > specfic low temperature "setting" period. In fact I
> > doubt that a gelatin solution can be dried without it
> > setting...
>
> You can dry gelatin in mostly sol form, which is easier to get damaged
> compared to geled material. This is rather easy to experiment - coat
> pieces of glass with plain gelatin and gelate one and don't gelate
> another. Then dry them.
>
> > (well I guess if you drove off all the
> > moisture you could... but that in itself would be
> > abnormal! not something you are likely to choose to
> > do.)
>
> If you dry the emulsion well above gelating temperature, this is what
> you'll get.
>
> > On the otherhand, if you are talking about the special
> > non-gelling gelatins, well... I hope you are not.
>
> I'm talking about inert, demineralized, type B photographic gelatin.
>
> > I understand you correctly... you just won't be doing
> > it at a particulary low temperature... most likely,
> > you will be doing it at night (wild guess)when the
> > temperature will be a bit cooler anyway.
>
> Even at night, the temperature in summertime can be as high as 30C.
> In this season, my darkroom is heated to 20C. Either way, I need lower
> temp to gelate my test gelatin dispersion. If you are coating less
> viscous emulsion, you'll need a lower temperature to gelate compared
> to more viscous emulsion.
>
> All these things are found in literature, for example, gelatin chapter
> of Mees and James, and also in Keller. They don't give actual numbers
> for temperature of gelation, because it varies a lot with gelatin and
> dispersion viscosity. On this part, I'm supplementing with info from a
> guy at Eastman Gelatine and also some testing with a gelatin sample
> from them.
>
> > Oh, and while I am here, s.o. asked if you or some one could use
> > denatured alcohol, for glass plates... well, it depends on the
> > reason, but in general, yes, denatured alcohol is usually ok, I
> > belive it is usully denatured with methanol or perhaps phenol, and
> > in either of these two cases it should be fine. (Don't Drink / Don't
> > Breathe);-)
>
> It's not me. I don't know why you need alcohol to make emulsion for
> plates... Or maybe you're talking about degreasing?
>
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