 |
|
|
 |
|
Taxidermy Freeze Dry |
 Because of the diversity of specimens being freeze-dried
for taxidermy purposes (from Brahma bull head mounts to
minnows used for fishing bait), trial and error has often
been the method used to determine how different taxidermy specimens
should be pre-frozen and freeze dried. The success or
failure often directly relates to the proper pre- freezing
of the taxidermy specimen, and the temperature at which the specimen
chamber is held during the drying stage. |
|
|
|
The Eutectic Temperature |
|
When frozen, various taxidermy specimens will totally solidify at
different temperatures. The temperature of complete
solidification is the taxidermy specimens eutectic (pronounced yu-tek-tic) temperature. The American Heritage Dictionary,
1969, defines eutectic as, "the lowest possible
temperature of solidification for any mixture of specified
constituents" An example of the variance found in
freezing temperatures is that of water - not all water
freezes at 32 degrees F. When water is contaminated with
other elements , such as salt, nitrogen, mercury,
industrial waste, etc., it's temperature of complete
solidification will change. Since one of the basic
premises if freeze dry taxidermy is animals are made up of
about 70% water by weight, the importance of eutectic
temperature is readily evident.
When determining eutectic temperatures, taxidermy specimens may
be divided into two general groups: those that contain
large amounts of body fats and oils (most fish, certain
species of ducks, amphibians, etc.) and those that do not
( the majority of mammals, reptiles, game birds, delicate
flowers, etc.) Because of the chemical makeup, taxidermy specimens
in the group (greasy specimens) require lower eutectic
temperatures than the second group (non-greasy specimens). |
|
|
|
Pre - Freezing |
|
Because natural salts are usually found in combination
with water in taxidermy specimens, pre-freezing should be done in
the shortest time possible. Slow freezing times lead to
salt concentration in the specimen resulting in lower
eutectic temperatures and increased chance for shrinkage.
Rapid freezing reduces salt concentrations and also
results in smaller ice crystals, which create less tissue
distortion. Rapid freezing may be obtained by freezing
taxidermy specimens in commercial freezers with temperatures of less
than -13 degrees F. (-25 degrees C.) it is generally more
economical to pre-freeze the specimens in a commercial
deep freezer, than use the specimen chamber as a freezer.
Freeze dry machines are most efficient when "drying"
frozen material, rather than initially freezing the
material, then drying it. The important factor in
pre-freezing any type of specimen is that the specimen is
completely frozen throughout. |
|
|
|
The Drying Stage |
|
Once the specimen has been prepared for preservation,
mounted, posed, and completely frozen, it is ready for the
drying stage. the important factor in the drying stage is
that the eutectic temperature is maintained. Because of
the lower eutectic temperature of greasy specimens, a low
processing temperature in the specimen chamber is needed
to prevent shrinkage. Generally this temperature should be
as 0 degrees F. and then raised even higher after a period
of time. Using these figures as guidelines, the
taxidermist using the freeze dry machine should determine
at what temperature his work is most successful. Some
factors to consider when analyzing proper processing
temperatures include: |
- Working in batch loads (all the same type specimen)
may be the most economical way to work, depending on
your own situation. Batch loads allow easy raising of
temperatures as the process progresses.
- When working with mixed loads (greasy & non-greasy
specimens) one initial temperature should be decided
upon (e.g. -5 degrees F. or 0 Degrees F).
- Some shrinkage may be traded off for speed. Mammals
may be run at slightly higher temperatures allowing
slightly faster drying times. The animals fur will cover
most of the shrinking that takes place.
- Not only does a variety of chemical make-ups exist
between different species, it may also exist between
members of the same species due to different diets, and
physical environments.
- Because if the lack of air to conduct heat within
the specimen chamber, some differences of temperature
will exist inside the specimen chamber itself. This will
require "rotating of the stock".
- The greatest water loss will occur early in the
drying stage when the dried shell is the thinnest and
offers the least resistance to water vapor movement.
|
|
The Economics Of Different Temperatures |
|
The rate of freeze drying is directly related to vapor
pressure. the higher the specimen chamber temperature is,
the higher the vapor pressure is at a given vacuum, and
the faster the drying is achieved. The rate of moisture
migration from the specimen chamber, to the ice bank, is a
also related to vapor pressure. The greater the
temperature difference between the specimen chamber, and
the ice bank. for example, a unit with the specimen
chamber set at 5 deg. F. and the Ice bank running at -55
deg. F., resulting in a temperature difference of 60 deg.
Will move moisture faster than the same machine with the
specimen chamber set a -5 deg. F., resulting in a
temperature difference of 50 deg. F. |
|
|
|
Dealing With Greasy Specimens |
|
Certain steps may be taken to raise the low eutectic
temperatures of greasy specimens. This will allow the
taxidermist to operate the freeze dry unit more
economically at higher temperatures. the first step is to
eliminate the extreme amounts of fats and oils that cause
the low eutectic temperatures. In the preparation stage, a
20 minute bath in a mixture of one cup of bicarbonate of
soda per gallon of water will assist in neutralizing fats
and oils. Also, injections of grease tallowfiers, such as
antioxidant will help in preparing greasy and oily
specimens for more efficient freeze drying. |
|
|
|
Analyzing Specimens |
|
Some of the questions that should be addressed when
considering the right temperatures to process a particular
specimen are: |
- What is the Physiology of the specimen?
- What is the Chemistry of the specimen?
- What solid mass of the specimen can be removed to
speed up the process, and not effect shrinkage?
|
|
If you analyze specimens with these questions in the
initial planning stages, problems can be eliminated. there
is nothing, to our knowledge, that can not be successfully
freeze dried without shrinkage, as long as it is freeze
dried at the proper temperature. |
|
|
|
Freeze Dry Taxidermy |
|
|
|
|
|
|
