The holidays is nothing if not cause to remember traditions. -K
In microscopy perhaps no slide is quite as traditional as the dry cell mount, a sealed air filled compartment protecting a dry object. Dry mounts took all sorts of forms from glass covered wooden slides, to full portions of insect, to diatoms and podura scales. However, of all the objects mounted dry perhaps none was quite so enjoyable (and now some common) as the mount of “Forams.”
Forams, or more accurately foraminifera, were among the most popular of the small fossil specimens to be mounted. In the present day one may be forgiven for questioning the designation as in the past it was somewhat of a common practice to label any small fossil thusly. The ease of acquiring them was no doubt a reason for their ubiquity. If one happens to live in an area that was formerly a body of water simply digging down a few feet in the garden (more about this come spring) will often reveal a layer of sediment full of a quantity of microfossils. Such were commonly mounted as an enjoyable object for examination with low power.
The traditional dry cell mount of forams is nothing more than a glass slip on which is mounted a specimen over an opaque surface. Around this is placed a cell, either a ready made one of aluminum (or these days of glass), or one built up of layers of shellac. The whole is covered by a circular cover glass which is sealed or cemented to the cell. The specimen may be then used as any other object for the microscope, secure from contamination and viewed as intended below a cover of recommended thickness.
To produce a traditional dry mount a few items will be required. Chief among them are a slide ringing table (for more on that see my earlier post on ringing a slide), a supply of round cover glasses, and a cell. For most practitioners the simplest means of producing a cell is by building one up from layers of shellac. One may use store bought, ready-made shellac of course, or the dry material dissolved in ethyl alcohol. If one is already possessed of an arbor press and a variety of circular punches one may form cells from aluminum with little trouble. Whether using shellac or aluminum one should fabricate cells so that they are only just thicker than the specimen vertically, and slightly larger than the cover glass diametrically.
For opaque mounted objects (such as forams) one will need a means of preventing light from penetrating the bottom of the slide. That need may be met easily by any matte finish black paint, though some practitioners will no doubt prefer to use black paper glued to the slip. One may try either and decide which is more to their liking, or trust to the greater convenience of either depending on the available equipment. With the contemporary popularity of scrap-booking circular paper punches may be had inexpensively and the chief argument against paper (the difficulty of true circles, discarded). Paper (of sufficient quality) is of uniform appearance and opacity throughout and lends itself to any number of adhesives. Paint is self adhesive in a way even modern gummed papers will never be and permits one to ensure perfectly central placement (as it is applied on the turntable), but may tend to be applied less then uniformly.
With a cell formed around the opaque disc one then affixes the perfectly dehydrated specimen so that it will not move. Historically, mounters used a variety of gum or albumen glues. Some in the present day may elect to use any of the plethora of artificial adhesives currently available, from rubber cement to cyanoacrylate the choices seem limitless. I confess to having always found tragacanth gum as the most effective and long lasting option. One need only add too a small quantity of the powdered resin (as it is commonly available) distilled water, which will then provide an effective and long-lasting adhesive that tends to prevent the condensation of moisture (by absorption of the same) in imperfect cells.
Do come by for the next (practical) post if you have any interest and in the mean time consider the application of the same methods for transmitted light mounts and other (think liquid without pressure) preparations as they will be elucidated some later time.