Hi Russ,

	Haven't had to sharpen one yet, but at $200 per reconditioning,
I will be using my Shandon knife sharpener for both the C and D profile
tungsten carbides (yes, one can use this sharpener for these knives!)
but that type of sharpening is not indefinite, you eventually have
to send it off for the big bucks reconditioning.  

I use mine for undecalcified bone sectioning, prefer the D profile,
with tape transfer (Instrumedics), this REALLY saves edges, I 
usually get fewer cuts to produce a usable section.  I guess the standard
answer is how much trouble you have cutting aka dull edge after many
samples (small) or fewer with large or dense hard cortical bone vs
trabecular bone. I trim on dull edge only, moving to the sharp
edge for sectioning - a "religious" fanatic on using this knife..  

Never use this precious edge on soft tissues, haven't tried
horses hooves.  The PMMA microtoming gurus should be able to give
some better answers on frequency of sharpening, my standard is still
if it isn't cutting well, move to a sharp edge.  This could be within
hours or weeks with the TC's, it sure pays to have an extra for a backup. 

For undecalcified bone cryostat cutting, my knife is a tungsten carbide
edge inset (or set into a steel back).  This gives a better heat sink
than a 100% tungsten carbide knife, and is still capable of being used
for GMA or PMMA on rotary microtomes.  

I tend to be very proprietary about who uses TC knives, since cost
to recondition is pricey, some individuals with heavy hands using conventional
blades get to look but not touch, and after seeing them massacre the tissues,
all TC work is mine.  Boy, is that attitude or what!  TLC with the TC has
kept mine off sharpener, so far, and a very low volume of bone.

I don't think I really answered the longevity question, still a judgement
call for me.

Gayle Callis