In a pinch one can get away with all manner of substitutions if any of the below is lacking, so don’t despair if one lacks some seemingly critical component. -K
Dry cell mounts can be somewhat labor intensive, particularly if only wet mounts have been produced in the past. A very small bit of practice goes a long way and attractive slides may be produced in no time at all. First, an accounting of the necessary materials;
- A small, perfectly dry, specimen
- A glass slip
- A circular cover glass
- A fine camels hair brush
- A ringing table
- Matte finish black paint, or india ink
- Tragacanth gum adhesive
- A wax glass-marking pencil
- A fine forceps
- A centering card marked with the cover glass size to be used
Preparing the slip
For many other mounts preparing the slip means only laying out a cleaned slip from ones supply. Dry cell mounts are rather more involved so are not generally made on a moments notice. For that reason one may wish to ready a quantity ahead of time, rather than a single slip.
To begin with one will need to equip the slip first with an opaque surface on which to mount the specimen, and then by building a cell around that surface to support the cover glass. Place a cleaned slip onto the centering card and use the wax pencil to mark the center of the slip and the borders of the cover glass. The side that is marked will be the bottom of the slip so immediately turn it over to prevent accidental use of that surface. With the slip so marked one needn’t worry if the ringing table to be used lacks a marking for the size of cover glass that will be used.
Place the slip onto the ringing table (make certain the marked bottom of the slip is down) and center it. Set the table spinning and mark with black paint a circle of sufficient size for the intended specimen. Some practitioners paint only a small area and some paint the entire are that will be covered, the choice is immaterial as the entire field of view is sure to be opaque expect if viewed with the lowest powers (30mm or more). In either case lay down a layer thick enough to obscure all light. In the beginning one may wish to lay down a few trials on a test slip that may then be removed from the ringing table and held to a light to determine the effectiveness of the paint. If bubbles or imperfections are evidenced in the painted disc one may generally remove them by lightly moving the brush from the edge of the disc to the center and back as it spins. Allow the slip a few moments to dry. One may remove the slip to a covered box and paint discs on a quantity of slips in preparation for the next step, or leave it upon the ringing table with an improvised cover if only one is desired.
Once the opaque disk is dry paint a ring of shellac around it so that the outer edge of the shellac ring is just larger than the cover glass to be used. Load the brush lightly with shellac so that it does not tend to drip. If the shellac doesn’t flow easily from the brush wet the bristles first in alcohol. Lay a second layer of shellac over the first almost immediately and then permit it a minute or two to dry before laying down the third and successive layers. A cell of considerable hight, 1/8th of an inch (3.2mm)or more, may be prepared in as little as 15 minutes The width of the completed ring of shellac forming the cell should not be more than 3/32nds of an inch (2.4mm) with 1/16th (1.6mm) being ideal. Once the cell is of a suitable height place it into a covered box to dry for several hours, overnight is ideal. If the ring is not dry when a cover is placed on it there will be a tendency for it to deform and run in towards the object.
The shellac used (and the quality of the brush) has the more to do with success or failure than skill. Always use a finely pointed, scrupulously clean brush, and make note of the shellacs viscosity. If the shellac is too thick one will end up draping threads of shellac across the interior of the cell. Alternatively, if the shellac is too thin building up a cell of sufficient height will take a very long time. Should threads of shellac evidence after a few minutes of prior success simply cleaning the brush can help. Above all one should work deliberately and resist the urge to rush.
Coming up next, part III; actual mounting!