Russ -
I can make a couple of comments, though I will not get into the "how long  . . 
. " debate.

Never use TC knives with wax blocks. Wax plucks TC particles and blunts knives 
fast.
Plastic resin or any of the freezing media make an excellent matrix and cutting 
those materials, TC knives last very well.
TC does not corrode in the cryostat environment they could be left in there 
indefinitely.
Ice crystals cause little wear on a TC edge. TC rates on the hardness scale 
only below diamond and is harder than sapphire.

Big TC knives have the tip section, which is pure TC glued to a SS base. That 
SS ought to be highly corrosion resistant too.
PST supplies pure TC blades, they are 3mm thick and require a holder. These 
blades are disposable and for many users they would be an excellent alternative 
to the larger knives.
Disclaimer: ProSciTech supplies TC knives and blades and so has an interest in 
their use.
Cheers
Jim Darley

ProSciTech                 Microscopy PLUS
PO Box 111, Thuringowa  QLD  4817  Australia
Ph +61 7 4774 0370  Fax:+61 7 4789 2313  service@proscitech.com.au
Great microscopy catalogue, 500 Links, MSDS, User Notes
                      www.proscitech.com.au

On Wednesday, August 25, 1999 3:14 AM, RUSS ALLISON 
[SMTP:Allison@cardiff.ac.uk] wrote:
> You may expect me to know this
>
> How frequently do you have to sharpen tungsten carbide knives.
> Yes, I know, how long is a piece of string!
>
> I appreciate comments on types of tissue cut - soft, calcified,
> horses' hooves, etc
>
> How about using them in the cryostat for undecalcified bone?
>
> All experiences gratefully received.
> Russ Allison, Wales