I had the good fortune to come across a copy of Grays Encyclopedia of Microscopy and Microtechnique at a local used book store a short time back and have been consulting it sporadically as inspiration strikes. One thing that somewhat surprised me (aside from how aggravating and inadequate the index is) is Grays thoughts on the placing of coverslips. Under the entry Whole Mounts, Zoological Materials subsection Mounting Specimens in Balsam he rocomends placing a drop of balsam on the slide, introducing the specimen and then "…lowering the coverslip horizontally until the central portion touches the drop. The coverslip is then released and pressed very gently until it just touches the top of the object." He then makes a very strong argument for why this method is superior and laments the method of placing coverslips which every other manual and guide I posses recommends, a method he calls unabashedly the "Wrong way…".
So now I'm curious, how does anyone else place their coverslips? Is Gray really a lone voice of dissent, or do I simply not posses enough liturature? Should I rush outside and try to locate an insect or two to test this out?
The conventional method, when dealing with a resinous medium and a whole invertebrate, is to first build up a cell (using a ringing table and shellac) or use slivers of broken coverslip to prevent the specimen from being squashed. The business of the cell may be skipped for only the slightest of specimens. A drop of the medium is then placed in the cell and the specimen is introduced. A coverslip is then lowered at an angle so that it may be held up on one side by a pin or brush. The pin or brush is then slid out of position and light pressure exerted on the coverslip. Ocasionally one is advised to keep pressure on the coverslip until the medium has dried.
The above is the method one will generally find everywhere from lab manuals to childrens handbooks, and it's all over the network. Essentially every guide I've seen on every website (even here!) varies only slightly from this procedure. Ostensibly one places the coverslip at an angle to prevent air bubbles from being caught under the glass.
Grays method claims to negate the requirement of a cell for specimens of a slightly larger size than might be otherwise possible and prevents the lateral motion one is frequently plagued by when using the other method. His claims (so far) seem to have been validated, some of them. I was unable to locate any appropriate invertebrate(s) outside (it's been snowing you know) but did find a few mites caught in a spiders web which I mounted according to Grays method. Results so far seem eminently successful and cursory examination with a hand lens shows no evidence of air bubbles.
I hope that you do begin to produce permanent mounts. It is a very rewarding part of the hobby and allows one to share their efforts even after they have passed away, just think the leaf or fly you mount today might delight a collector a hundred years from now!
So far the two mounts I've produced using Grays method seem to be (updates in a few weeks when they have set) bearing up his claims admirably with no undue shrinkage or air bubbles. I must however pursue this further at least for my own curiosities sake. It seems unlikely I will be in a position to capture live specimens of a suitable size in the near future so I may resort to purchasing some small ants or similar live from a biological supply house. I wont be able to consider Gray validated until I've been able to put a number of suitable specimen through the whole process (FAA, ETHO series, xylol, balsam). I suppose I might have put the specimens from the spiders web through a ETHO series but it seemed rather pointless… in any case updates to follow.
I expect that the catch with Gray's method is that the cover slip has to go absolutely, perfectly flat onto the specimen. It is possible that complete satisfaction of this stringent requirement leads to impeccable results.
On the other hand, if one misses by whatever small degree, then the conventional option – properly executed – may yield good results as well. In this latter case, one would be well advised to find the best angle of inclination, applied pressure and so on depending on various factors such as specime size and shape, mounting media, dexterity and available tools.
I would suppose that in a corporate setting one has little say in which method is employed, but we hobbyists don't have to always obey whatever procedural constraints, so, yes, experimenting with Gray's method sounds to me like a great idea!
It seems that the most important aspect of Grays method is viscoscity. I've tried quite a few now and have had my share of terrible and beautiful results. With too much solvent in the medium the specimen ends up getting damaged while not enough does lead to air bubbles. The conventional method has the benifit of speed, as unless you start with a thicker balsam it's nessicary to allow it to thicken on the slide for a time in a dust free environment (or idealy in an incubator). A day on my bench under a bell jar seems about right for a suportive medium that really lets Grays method shine.
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