6.10.
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209
clean glass surface, and can be stripped from this base. It does not seem
possible to obtain consistently a satisfactory glass surface by chemical
cleaning, but extreme heat suffices. An ordinary 1x3 in. microscope
slide is used. It is heated in a Bunsen flame until the glass actually begins
to melt and bend, and the edges become fire-polished. Such a prepared
glass surface is used immediately. It has seemed to this writer, however,
that it is harder to separate carbon films from this surface than from mica.
Kafig (1958) has proposed an ingenious method of preparing a glass
surface so that carbon films can be stripped from it. He advocated first
depositing a layer of the dye, basic fuchsin, on the glass and then evaporating carbon on top of this. Subsequently the dye is dissolved and the
film can be stripped. The method depends partly upon depositing the
correct amount of basic fuchsin in the first place. The stock solution consists of 3 gm of the dye in 150 ml acetone, to which 1 ml nitric acid and
l A ml Aerosol OT 25% detergent is added. A standard microscope slide is
dipped in this, drained and dried. After the carbon film has been deposited, the slide is soaked in acetone, acidified by the addition of 5%
acetic acid, until the color disappears. The slide is then dried, after which
the carbon film can be floated off. (This procedure was not completely
described in Kafig's published report.)
Efforts have been made to coat glass with thin films of glycerine or
liquid detergents with low vapor pressures, and then to deposit and strip
carbon films on and from such surfaces. No doubt such methods work on
occasion, but are hard to standardize.
Pure carbon films are extremely brittle and will not stand stretching.
Thus, grids with carbon films upon them must not be bent unless one is
willing to sacrifice the film in some of the squares.
6.10. "Sandwiched" Sections
It has already been stressed that conventionally mounted methacrylate
sections may exhibit a fine-order artifact that destroys macromolecular
detail (Chapter 4.8). This results from the melting of the methacrylate
during electron bombardment, and consequent surface tension effects.
Figure 9 indicates how much of the embedding medium actually disappears during observation, and it is easy to understand how delicate structures at the exposed surface can collapse. Thoughts about this led Watson
"SANDWICHED" SECTIONS
209
clean glass surface, and can be stripped from this base. It does not seem
possible to obtain consistently a satisfactory glass surface by chemical
cleaning, but extreme heat suffices. An ordinary 1x3 in. microscope
slide is used. It is heated in a Bunsen flame until the glass actually begins
to melt and bend, and the edges become fire-polished. Such a prepared
glass surface is used immediately. It has seemed to this writer, however,
that it is harder to separate carbon films from this surface than from mica.
Kafig (1958) has proposed an ingenious method of preparing a glass
surface so that carbon films can be stripped from it. He advocated first
depositing a layer of the dye, basic fuchsin, on the glass and then evaporating carbon on top of this. Subsequently the dye is dissolved and the
film can be stripped. The method depends partly upon depositing the
correct amount of basic fuchsin in the first place. The stock solution consists of 3 gm of the dye in 150 ml acetone, to which 1 ml nitric acid and
l A ml Aerosol OT 25% detergent is added. A standard microscope slide is
dipped in this, drained and dried. After the carbon film has been deposited, the slide is soaked in acetone, acidified by the addition of 5%
acetic acid, until the color disappears. The slide is then dried, after which
the carbon film can be floated off. (This procedure was not completely
described in Kafig's published report.)
Efforts have been made to coat glass with thin films of glycerine or
liquid detergents with low vapor pressures, and then to deposit and strip
carbon films on and from such surfaces. No doubt such methods work on
occasion, but are hard to standardize.
Pure carbon films are extremely brittle and will not stand stretching.
Thus, grids with carbon films upon them must not be bent unless one is
willing to sacrifice the film in some of the squares.
6.10. "Sandwiched" Sections
It has already been stressed that conventionally mounted methacrylate
sections may exhibit a fine-order artifact that destroys macromolecular
detail (Chapter 4.8). This results from the melting of the methacrylate
during electron bombardment, and consequent surface tension effects.
Figure 9 indicates how much of the embedding medium actually disappears during observation, and it is easy to understand how delicate structures at the exposed surface can collapse. Thoughts about this led Watson