An Old Method of Mounting Radiolaria
Sometimes we use our own methods of mounting things that are perfectly satisfactory but occasionally when reading through old literature from the Victorian era we chance upon a method that really is excellent and much better than what we have. This is a description of just such a method from that age, which is equally suitable for use in dry mounting as in Canada Balsam.
Is begins with having a sieved washed sample of Radiolaria that has first been washed in acid and looks clean and bright in good light, before mounting.
Preparation is as with most things the key to success. Quality 3X1” glass slides need to be well washed and quality Gum Tragacanth as well as a ringing table is required.
Mountng in Resins such as Canada Balsam or Eukit.
The Gum Tragacanth solution must first be prepared . I use the lid of the gum jar as a painters pallet and add one very small portion of gum to a large pool of distilled water on the lid. When the gum is fully dissolved there must be no blobs of mucilage visible. If there are any blobs, use a pipette to suck them up and add more water, until nothing is visible in the fluid.
The clean 3X1” slide is placed on the ringing table and a little paintbrush is used to run a circular pool of gum water onto the centre of a rotating glass slide. Check that the circular disk of gum/water is stable, sometimes it prefers to run off into pools. Then perhaps the suface is contaminated and an alcoholic wipe might help.When the liquid is correct, dry it off with gentle heat until quite dry. One should be able to see a dried up but complete feint disk of dry gum . If it is too white and prominent, wash it off and try again with less gum or more water. Remember, that the dried up disk of gum will become the same diameter as the completed strew of Radiolaria.
Then make sure the slide is cool . Here a cold plate from a fridge might help, and breath on it. Ones breath should condense on the glass in droplets but the disk of gum will become slightly liquid, as it absorbs moisture. Then pour the shells from a Petri dish onto the central disk quite thickly and then invert the slide smartly over the Petri dish so that most of the loose shells return to the dish. Tap the glass to make them fall. Then use the warmth of a lamp to dry the thing off fully and again invert the slide over the Petri dish so that the shells that landed on the liquefied gum remain, but those that landed on damp glass now fall, having dried out. One should now be looking a a clean disc of Radiolaria surrounded by clear glass. Make sure that the whole slide is dry by heating under a lamp.
Then a resin like Canada Balsam thinned with a little Xylene is dropped on the middle to help expel the air from the shells. Then place a drop of thicker Balsam or other resin over the shells and lower a cover slip.
This may seem to be quite a performance for a tiny circle of Radiolaria, but it will be worth the effort. The resin may then be dried off with heat in the usual way, and the slide labelled.
Dry Mounts may be constructed in a similar manner but first an aluminium ring must be cemented to the glass and a black background must be laid and dried . More care is needed in any heating or the paint may be damaged. The circle of gum-water can then be laid using the ringing table. When this is successful the same procedures can be followed but without the Canada Balsam or other resin of course. This same system can also be used to renovate a very old slide that has through the ravages of time become thoroughly unsuitable for use. The method itself was I know learned from a very old book but I am afraid that I have long forgotten the reference or the original author of the idea.
Image to follow next weekend, hopefully BD