SAFE MICROSCOPIC TECHNIQUES FOR AMATEURS

I - MOUNTING MICROSCOPIC SUBJECTS.

Part 5: Summary of Parts 1-4

WALTER  DIONI                       Durango (Dgo) México
 

Articles in the series
Part 1: Introduction - liquid media.
Part 2: Soldifying media.
Part 3 - Mixed mounting media - Part A; fructoglycerol and modified Brun's medium as mountants
Part 3b. PVA-lactic acid and PVA-glycerol
Part 3c - Gum arabic media
Part 4 - Glycerin jellies

 

Finale


If you count them you must arrive at 20 safe mounting media discussed in this series. They provide mounting media for all the materials you may wish to prepare. You don’t need, even for a medium term of permanence (5, 10, 20 years?) to have resort to the expensive Canada Balsam. And remember that, even if this mountant cannot be excessively dangerous because of the few occasions you may use it, and the small quantities involved in any mounting operation, the real danger is from the solvents (all of them toxic, and flammable) which you must store and use when required.

Leave the Canada Balsam for the professional taxonomists that legitimately search for 'HYP' (Hundred Years Permanence) for a type species, and have lots of fun time making your collection of really professional looking slides.
 
List of experimental mounting media

AW, antiseptic water: sample water with added fixative
PG, pure glycerin
FMM, fructose mounting media (Karo, or Larry’s fructose)
CPG-pva, Commercial Pure Glue, based on PVA
AG, alcoholic glycerol
FG, Fructose glycerol medium
FGL, lactic fructose glycerol
APT, von Apathy Gum Syrup
GAF, Gum Arabic Fructose.
GG, Glycerinated Gum
GLG, Glycerinated Lactic Gum
PVA-L, PVA formula with lactic acid for high clearing action
PVA-G, PVA formula with glycerin, for a mild clearing action and less acidic medium
GJ, Kaiser’s Glycerin Jelly
BJ, Borax Jelly (Fisher’s type glycerin jelly)
FJ, Fructo-jelly
CGJ, chromed glycerin jelly
NPM, Nail polish mountant
Norland 61, a synthetic commercial glass-adhesive of high refractive index
(DAMAR), gum Damar, diluted in Turpentine, or in Toluene

solidifiable media

liquid media
natural or synthetic resinous media


SELECTING A MOUNTING MEDIA

It is possible that only Canada Balsam has the 'HYP' record, but if you are not a professional taxonomist trying to preserve type species for the eternity, who cares?  And certainly the much cheaper Damar (diluted in Xylene or in Essence of Turpentine) can compete for the professional mountant title and (in turpentine) it is safer than Balsam.

But I have given you 6 products that work directly from the container, (PG, KMM, NPM, CPGpva, AG, and Norland 61) and another 14 formulae for safe mountants, most of whose prepared slides can be filed for months, even years, some for decades. So which one of them must you use?

Almost any one of the revised media can do a good job as pictures in this article series have shown.

But nobody needs a complete set of mounting media. People are selective and each amateur has vocations and interests centered on some groups of subjects.


This is my own discriminating analysis:
 
      

The most difficult to use.-

1) Two of them (AW and PG) although very difficult to use, are indispensable for all those that like to work with 'pond samples', invertebrates lab cultures, and similar materials. You must learn to work with them, especially to seal them in a reliable way. Pure Glycerin when VERY WELL SEALED is a professional quality media, filed in museums for decades.

2) In my opinion the other difficult ones are the group of 4 media of Gelatin Jellies. They have been handed down from folklore, coming from the 19th century, and certainly they are the most often proposed media for the amateur. But you need to melt them in an appropriate apparatus (most certainly you must make your apparatus) and even with some risk if you use gas or alcohol, open flames, matches or cigarette lighters. You frequently must filter them to have a really clear and clean medium, and fight against the ever present air bubbles under the coverslip, and they are thermally unstable, needing special care to store them and the slides made with them.

I must be convinced that my subjects cannot be mounted in other media, or that gelatin is the utmost media for some subject, for me to use it. As an example, mount a “daphnia” in Kaiser Jelly and in PVA-G, the lesser refractive jelly mount gives you a sense of depth that the PVA does not.

The less safe.- Gum Damar, although a relatively cheap and efficient medium, with good optical qualities and a predictable life of about the 100 years, is not a totally safe medium, and must be prepared and used by younger amateurs under adult supervision. It should be recommended only for grown ups, and very careful amateurs. But it really merits becoming a professional standard medium.

The specialized one.- The Norland 61 synthetic medium although having only a medium high refractive index, is the safe alternative for those that want to try the beautiful and difficult diatoms.

The medium rating.-  CPG, AG, FG, FGL, and GG, although each have some good qualities they are not top quality, especially because of their poor drying behavior. If there are better mountants, why use them? But try them with your subjects before you leave them aside.

The best media.- Of course they are the remaining 7 media and can be split in two clear cut groups:

1) FMM, GAF, and even APT are cheap aqueous media, easy to buy or to make, dry well and useful for most of the subjects you can work with.

FMM (in the Karo, or Larry Legg’s version) is probably the best general medium for young amateurs' work, and even for many professional jobs, being highly versatile and having many of the qualities of Glycerin, as well as preserving the green color of chlorophyll for a while (if you fix your vegetable tissues with an adequate fixative). A 60% water solution of the commercial syrup is the more easy to use and best drying medium. I do not know how good the permanence of Larry Legg’s fructose medium is, but Karo evidently has a very good antiseptic (safe, because it could be eaten).

GAF and APT, have many good qualities and have the same applications as FMM, but they need to be manually prepared, and stored with an antiseptic, and are not better than FMM.

2) NPM, GLG, PVA-L, PVA-G, is a special group of media that imparts to the mounted subjects a high transparency. And all of them have very good and most similar qualities, including very good optical and drying properties.

NPM is the most expensive, but the easiest to find and buy. For the others you need to get lactic acid (which seems to be not so difficult to obtain) and PVA (Polyvinyl Alcohol). If you can buy the professional grade PVA, it gives you the capacity to adjust the density of your medium. In my experience to get PVA commercial glues seems not to be a problem. In only two searches (one in NY and the other here at Durango) I found two commercial transparent PVA paper glues. Not to be confused with the white glue that is also sold as PVA (Polyvinyl Acetate).  I think PVA-G that does not need lactic acid, is also the best option for mounting some little creatures in which I am very interested, like tardigrades, rotifers and gastrotrichs, having the advantages of Glycerin Jellies and none of its defects.

PVA-L. and GLG are the best alternatives to the much used but dangerous Hoyer’s medium, with many advantages for the PVA-L formulation. When using them, if you make the formulas with PVA commercial glues, take care to replenish the media under the coverslip at frequent intervals until they stabilize. Then seal with care.

My mounting media favourites

Of course I use the AW method, and also use glycerin (PG) either as a mounting medium or as a clearing agent, or as an intermediate medium. I use Karo as a 'Jack of all trades', and NPM as my resinous mountant (well…when I remember that I am a grown-up, I also indulge myself with some special mountings with Damar) having at hand two additional little bottles of PVA-L, and PVA-G, made with commercial paper glue.


There is no one subject including histological or botanical sections (Karo, PVA-G) that I couldn’t mount. (….except diatoms!) And I no longer have the problems of dehydrating, using solvents, heating slides and coverslides, using antiseptics, or slipping coverslides, or need stoves to dry slides.

And I even could use the Karo and the PVA-G formulas in the same way as the glycerin for step to step concentration when I try to mount my mixed collections of microinvertebrates (see the discussion of AW in the first part of this series, or the similar discussion on mounting GALA fixed materials in the first article on safe fixatives).

This is my advice for a cheap and safe set of mounting media, but which you select for your own favourites, is up to you. Experiment and select the mounting media that is best for the subjects in which you are most interested. You have 20 choices at your disposal.


NOTES:

I prepared most of the investigated media more than eight months ago. I used Listerine as my preferred antiseptic. None of the Listerine treated formulas had developed fungal infections but the Borax Jelly does after they melted in summer temperatures.

I left half the von Apathy sucrose formula, and half the Fisher Borax Glycerin Jelly with double borax without adding Listerine to either. Both of them are now heavily contaminated. And I assure you that the Von Apathy smell is not good. Not in my country and possibly not in Europe, but G. Couger tells me that the best antiseptic for the Jellies, Phenic Acid (Phenol), is easy to obtain in the United States. Add 1% w/w after finishing the preparation of the medium.



Comments to the author,
Walter Dioni , are welcomed.


 

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