Re: Shopping for Hardeners

From: Rhody Simpatiko <aunt_rhody@oldgreygoose.com>
Subject: Shopping for Hardeners
Date: Thu, 19 Jan 2006 05:56:52 -0800 (PST)

> Thank you for this helpful summary of hardening agents. Could I impose
> upon you to share your thoughts on about chrome alum? How does it rate
> according to your 10 criteria? Toxic, yes. But cheap, non-volatile and
> fast. Correct?

From: Ryuji Suzuki <rs@silvergrain.org>
Subject: Shopping for a hardener (Re: Glyoxal?)
Date: Wed, 18 Jan 2006 18:36:39 -0500 (EST)

> (1) crosslinks gelatin to reduce swelling factor to 5x or less
> (2) crosslinks gelatin reasonably fast
> (3) crosslinks gelatin in wide range of conditions (robust reaction)
> (4) does not compromise archival properties
> (5) has relatively low toxicity and manageable risk in case of accidents
> (6) has low environmental load (when inactivated prior to disposal)
> (7) has reasonably long shelf life
> (8) is preferrably nonvolatile
> (9) is preferrably inexpensive
> (10) is preferrably commercially produced and available
>
> No known hardener meets all of them.

Chrome alum fails 2, 3, 6.

One problem I have with chrome alum is that, the viscosity of
gelatin-alum mix becomes very viscous. This is not very easy to
handle. Glut can increase the viscosity somewhat if the gelatin
concentration is high, but bisepoxide doesn't do this.

Chrome alum works best on alkaline side of isoelectric point (5 for
lime treated cattle bone gelatin, but not very well defined for acid
treated pigskin gelatin, though pigskin's pI can be as high as 9), but
chrome alum will precipitate and become inactive at high pH. So the
window of optimal pH is actually very narrow and tricky. Reaction of
chrome hardening is pretty slow. So people tend to put a lot of it,
and then they'll face afterhardening.

Glut and other organic compounds can be readily destroyed to make
inert form before they get dumped down the drain, but chrome alum is
still chromium no matter what. Sure it's not as bad as hexavalent
dichromates but I generally prefer to minimize unnecessary risk.
Received on Thu Jan 19 16:26:46 2006