4.11.
EPON EMBEDDING
113
to be made. In humid environments it may also be desirable or necessary
to dry carefully the gelatin capsules before using them as the final molds.
This writer has heard complaints about Epon resins deteriorating significantly in about a year's time. Such reports are hard to evaluate, however, for one does not know the conditions of storage.
Epon mixtures, complete with included accelerator, can be stored
frozen for relatively long periods of time which is a decided convenience.
Minick (1963) recommended a —40° or —50°C temperature, but in our
own experience such an extreme cold seems entirely unnecessary. We have
been using the freezer compartment in a household refrigerator for this,
and find that — 10°C is sufficient for storage for at least a month. There
does occur a very slow thickening of the mixture which makes one distrustful of using it after perhaps 2 months. More recently we have been
using a — 35°C freezer, and apparently the mixtures keep indefinitely.
A very convenient way of freezing and storing an Epon mixture is to
divide it into 10 ml plastic disposable syringes. These are filled so that
there is a minimal amount of trapped air, and then the hole in the stem
is plugged with a toothpick, and recapped. For use, the loaded syringe
need only be warmed to room temperature, and the syringe as a dispenser
makes it possible to handle the Epon neatly.
Earlier attempts to control the hardness of Epon blocks include those
of Kushida (1959) and Finck (1960). The latter author, like Luft, tried
blending two different anhydride hardeners to produce a satisfactory end
result. He also tried as a variation incorporating a chemically bound
"flexibilizer" (Gardolite NC 513) to counteract the hardness produced by
the hexahydrophthalic anhydride hardener used with it. Kushida's effort
to produce a similar result depended upon blending two different Epon
resins (815 and 812, the latter originally designated 562) which produce
plastics of different hardness. This writer has not had experience with
these techniques.
There have been difficulties in sectioning Epon that I think must be
blamed upon the Epon itself, although I cannot say whether it is just a
matter of its water content. The most serious of these probably result
from surface displacements while sections are being cut. The end effect
FIG. 10. Apical region of a cell of the proximal tubule of a rat kidney. This material
was fixed first in buffered formaldehyde, followed by buffered osmium tetroxide. It was
embedded in Epon and stained with alkaline lead hydroxide. Compare with Fig. 7.
The large crystalline mass (arrow) is a typical lead carbonate contamination formed
at an air interface with the staining solution. The small encircled crystals presumably
are also lead carbonate, but formed in the bulk of the staining solution, probably from
contaminated sodium hydroxide.
EPON EMBEDDING
113
to be made. In humid environments it may also be desirable or necessary
to dry carefully the gelatin capsules before using them as the final molds.
This writer has heard complaints about Epon resins deteriorating significantly in about a year's time. Such reports are hard to evaluate, however, for one does not know the conditions of storage.
Epon mixtures, complete with included accelerator, can be stored
frozen for relatively long periods of time which is a decided convenience.
Minick (1963) recommended a —40° or —50°C temperature, but in our
own experience such an extreme cold seems entirely unnecessary. We have
been using the freezer compartment in a household refrigerator for this,
and find that — 10°C is sufficient for storage for at least a month. There
does occur a very slow thickening of the mixture which makes one distrustful of using it after perhaps 2 months. More recently we have been
using a — 35°C freezer, and apparently the mixtures keep indefinitely.
A very convenient way of freezing and storing an Epon mixture is to
divide it into 10 ml plastic disposable syringes. These are filled so that
there is a minimal amount of trapped air, and then the hole in the stem
is plugged with a toothpick, and recapped. For use, the loaded syringe
need only be warmed to room temperature, and the syringe as a dispenser
makes it possible to handle the Epon neatly.
Earlier attempts to control the hardness of Epon blocks include those
of Kushida (1959) and Finck (1960). The latter author, like Luft, tried
blending two different anhydride hardeners to produce a satisfactory end
result. He also tried as a variation incorporating a chemically bound
"flexibilizer" (Gardolite NC 513) to counteract the hardness produced by
the hexahydrophthalic anhydride hardener used with it. Kushida's effort
to produce a similar result depended upon blending two different Epon
resins (815 and 812, the latter originally designated 562) which produce
plastics of different hardness. This writer has not had experience with
these techniques.
There have been difficulties in sectioning Epon that I think must be
blamed upon the Epon itself, although I cannot say whether it is just a
matter of its water content. The most serious of these probably result
from surface displacements while sections are being cut. The end effect
FIG. 10. Apical region of a cell of the proximal tubule of a rat kidney. This material
was fixed first in buffered formaldehyde, followed by buffered osmium tetroxide. It was
embedded in Epon and stained with alkaline lead hydroxide. Compare with Fig. 7.
The large crystalline mass (arrow) is a typical lead carbonate contamination formed
at an air interface with the staining solution. The small encircled crystals presumably
are also lead carbonate, but formed in the bulk of the staining solution, probably from
contaminated sodium hydroxide.