Re: Help with what I believe is a hardening issue

Christina Z. Anderson wrote:

> OHHHH, Tom, my very very bad! Thanks for clarifying.
>
> Question, though: for our purposes of hardening gelatin, does
> paraformaldehyde not work?? Could we not mix up a solution of the
> powder in water at time of use and throw? Or will it not harden the
> gelatin?? And, if we can mix up a solution of it that can do the job
> of formaldehyde, is there a percentage you would suggest?
> Chris

Hi Chris,

Without heating and increasing the pH, there is no way you can tell the
resulting consentration of formaldehyde in the solution. Some will will
always be dissolved, but you will have very little control. If you just
mix the powder in the water, you will have a suspension of
paraformaldehyde particles in a weak formalin solution. The actual
consentration will be depending on pH, temperature and whatever else is
present in the water. This may, or may not do the job for hardening. I
wouldn't use it. There are enough variables in alternative processes to
avoid introducing unnecessary ones.

A properly made solution of paraformaldehyde is clear, with only
residues of cloudiness, which needs to be filtered out. If you use a
cloudy "solution" (i.e. suspension), you may leave particles of
paraformaldehyde embedded in the gelatin. This can result in gradual
release of formaldehyde over time, esp. if the RH is high. I don't know
how this will influence the emulsion in the long run, but it is hardly
likely to be beneficial!

Much better to just buy a small bottle of commercial formalin every now
and then. Even p.a.-quality (p.a. = pro analysi) is not very expensive
(about $18,-/liter here in Norway, probably less in the US).

Best regards,

Tom Einar
Received on Wed Nov 10 10:13:10 2004