With regard to the various comments re celloidin.

Celloidin is a sulfated and nitrated cellulose which can be used in
solution
to infiltrate small to medium sized specimens. It can also be used in
0.5-1%
solution as a covering over sections to retain difficult section on
slides.
Pros for celloidin use are that as infiltration is at room temperature,
shrinkage and distortion is significantly lower than using paraffin wax
(around 5%). . It is expensive, has VERY  long infiltration times and is

technically much more difficult than paraffin wax. Sections when cut
must be
stored wet usually in 70% ethanol.
Celloidin  is also impervious to enzymes and some stains so must be
removed
if using these. Will also stain permanently with some stains such as
celestine blue.

Low Viscosity Nitrocellulose (LVN) powder can be dissolved in solvents
to
higher concentrations and will infiltrate somewhat faster. It is used
for
larger specimens. It has however much lower strength and tends to
separate
from sections and to fragment to a greater degree than celloidin.
LVN is unsuitable for covering sections.

Before deciding what to use and where to purchase "celloidin", you
really
need to determine its use.
If larger specimens then LVN would be my choice, if smaller then
celloidin.
Do you have a time limit for production of the sections?  Do you have
expertise in celloidin cutting, mounting and staining?

There is really another alternate, double embedding. For tissues that
are
friable and for certain applications can use Peterfi's technique. This
involve an infiltration in low concentration of celloidin usually in
methyl
benzoate, clearing (and also hardening celloidin) in toluene or xylene
(he
originally used benzene) and then  infiltrating in paraffin wax. The
celloidin tends to hold tissue together to greater extent than paraffin
wax
alone.

A further point. Many states will no longer allow shipment of celloidin
as
solid strips or LVN as a powder due to their explosive nature when dry
and
often will only ship solutions.
LVN must be kept moist generally with n-butyl alcohol.
Celloidin strips will deteriorate upon prolonged storage and are best
kept
moist with alcohol.
Barry