Wayde Allen (wallen@boulder.nist.gov)
Thu, 03 Jun 1999 17:07:01 -0600 (MDT)
On Thu, 3 Jun 1999, Judy Seigel wrote:
> Wayde, I may be wrong here, but as I recall the question it didn't come
> with a medium attached, but was about bloom v. hardening, although perhaps
> there was an antecedent I missed.
The original question was:
On Tue, 1 Jun 1999, Paul Lehman wrote:
> 2 quick questions:
> Can someone give me a short definition of the Bloom rating for
> gelatin, and
>
> Is gelatin sensitivity to dichromates a function of the
> bloom rating?
No there wasn't a mention of the intended medium, but there definitely
wasn't a mention about gum either, hence my confusion with your reply.
> I certainly don't say or believe that "all bets are off." I simply point
> out that the gelatin exists not in the abstract, but embedded in a matrix
> of other quantities & qualities, so that, it seems to me, not possible to
> isolate a given ratio without saying under such & such conditions.
Aren't you the one who always is harping on minimizing variables <grin>?
I figure I can only provide what little I know about the question that was
asked. It isn't too profitable for me to make guesses about the other
guy's process.
> If the bloom v. dichromate is X factor with use of one gum arabic it
> might very well be 2x with a different gum arabic.
I have a really stupid question, is there even such a thing as a bloom
rating for gum arabic? I'll have to go look at my bottle of gum, but I
thought that gum was rated primarily in degrees Baume'. I can't exactly
envision a bloom test for gum.
> But now that you make clear that
> you refer to carbon, perhaps the factors are less interdependent. Still, I
> would imagine that the color, for instance, and/or the actual pigment, has
> its effect.
I don't think that we are in disagreement here, but again that wasn't part
of the original question as I understood it.
> I'm afraid I don't follow you here, but again, if you're talking about
> hardening I assume you consider exposure a variable. Practically
> speaking, thicker emulsion requires a longer exposure, although I suppose
> theoretically the top part of it hardens at the same rate as with thinner
> gelatin. Perhaps that's all you're concerned with...
Yes, that the top rate hardens at the same rate is all I'm concerned with.
I'm more interested in the issue of how hard is hard.
> So is the hardening purely mechanical? I wouldn't have thought so.
No, that is my point. You can't really expect a test of mechanical
properties to tell you much about chemical properties, although there may
be some interplay between them.
> I have same bloom gelatin from different animals (and the "porcine" is a
> lulu) that behaves very differently, although that's in general. I never
> measured only hardening.
Chemically they will almost certainly be different, mechanically they
should behave similarly.
> > Like I said in my original post, and this one too, I'm not convinced that
> > the bloom number has much to do with the the sensitivity of the gelatin to
> > dichromate hardening.
>
> Yes, I'm not either.
As usual it sounds like we are in violent agreement <grin>.
> In my own experience, in which control was let's say general, but not
> fanatic, temperature of the coating solution was a bigger variable than
> bloom, though again, I imagine that coating a thick layer for carbon is
> different from just applying a size.
Again, I don't think I'd expect the bloom number to indicate the gelation
temperature. I think we have to be careful to understand exactly what you
get from any given metric.
> It seems possible that gelatin plasticized like roll film would not
> differentially harden and melt in the ready way carbon tissue does.
OK, why not? You could be right, I just don't know ... yet <grin>.
- Wayde
(wallen@boulder.nist.gov)
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