> A mixture of equal parts of 100 bloom and 300 bloom gelatin acts like
> a 150 bloom gelatin in the very important quality of how much water it
> will absorb. As most people know, a 100 bloom gelatin will absorb much
> less water than one of 300 bloom (this is why formulas for making carbon
> tissue show such varying percentages for the gelatin solution, or at
> least one of the major reasons). A mix of the two will absorb more water
> than the 100 bloom by itself, less than the 300 bloom by itself. This is
> perhaps not a real definition of bloom, but it does offer a practical
> explanation for what happens in actual use (at least as most of us
> use gelatins, to size papers, make carbon tissue, prepare emulsions, etc.).
>
The definition of the bloom factor that I have always understood has
to do with a gelatin's "hardness" or "stiffness." As I recall (please
correct me if I'm wrong) the bloom factor of a batch of gelatin is
measured by dropping weights onto a block of the congealed stuff.
The resistance of the block of gelatin to the weight indicates its
bloom.
The area where I found the bloom of gelatin to be a factor was in
preparing collotype plates. The higher (or harder) the bloom, the more
"jagged" the reticulation pattern of the finished plate. The softer the
bloom, the more even and elongated the reticulation pattern. Until I
read Sandy's description above, I never knew that bloom also affected
the ability to absorb water. Also, in response to the original
question, I have no idea how mixing different bloom gelatins might
affect the reticulation pattern as I never tried it.
Interesting what you learn...
Carson Graves
carson@ileaf.com