FotoDave@aol.com
Fri, 04 Jun 1999 10:37:06 -0400 (EDT)
Paul,
I have a feeling that since we know so much and so little about gelatin,
everyone is talking / repeating about the same thing here although some of
the data might seem contradictory.
> Specifically, Knox gelatin worked fine but a
> generic grocery brand of gelatin proved to be only half as sensitive.
What do you mean specifically by half as sensitive?
> On the surface this seems contradictory. If a 7% concentration of one
> gelatin gives a bloom rating of X, and a 7% concentration of another
> gelatin gives a bloom rating of Y, how can the bloom rating be
> proportional to the concentration if the solutions were prepared at the
> same concentration?
I think maybe they might the strength of the original gelatin and the
strength of the solution?
> Thus the bloom rating may
> only be an indicater of water content of the dried granules (similar to
> hydrated salts).
Yes, but I believe since gelatin has continuous chain, it is hard or
impossible to define molecule as in salt, but my knowledge in gelatin is
really limited.
> If I have read the responses correctly, it appears that this issue has
> not been specificly addressed in a controlled study (although it may be
> in the deep literature somewhere).
Sandy mentioned that the sensitivity is related to dichromate strength but
not the *type* or the *strength* of the gelatin and that this can be easily
demonstrated. Maybe Sandy could give us some details on what this exactly
means or how it can be demonstrated.
> So, my guess is that dichromate sensitivity may be a function of Bloom
> rating. Those factors that may influence bloom rating should also
> influence dichromate cross-linking of the gelatin (gelatine size, shape
> and availability of functional groups). However, the degree of
> sensitivity corrilation to the bloom rating is the final question.
I think we might be mixing different thing. One might claim that the
sensitivity is the same regardless of the strength. By that maybe it is mean
that the same amount of gelatin is hardened. But in application in
photography, sensitivity might be defined differently. For example, a thicker
gum *might* be same sensitive as the thinner gum in the technical sense, but
since the thicker gum will coat thicker, the top coat will wash out, so if
one define photographic sensitivity according to the step where the tone
starts to appear, then one gum might be considered "slower" or "less
sensitive." So we are talking about the same thing yet different things.
Dave S
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:36