Crystals and Polarization: 
A Few Additional Thoughts

by Richard L. Howey, Wyoming, USA

 

 After writing my earlier article on polarization, I remembered that I had a slide box with over 60 preparations that I had made over the years.  There were many more that I made and discarded, but these were of sufficient interest to keep.  Usually when I get a passion to look at crystals, I make 15, 20 or more preparations of different chemicals and, stupidly, I don't always follow my own advice, so some of the most spectacular slides are unlabeled and I have no idea what's on them.  Nonetheless, they are too impressive to discard.  So, do label each slide, even when it's one that you think won't be interesting and even when you regard it as a temporary, a quick preparation, because inevitably, one of those slides will turn out to be a stunner and then 5 years later, you won't have the vaguest idea what it is.

 Fortunately 90% of the ones in this box are labeled.  I had only recently acquired the 1/4 and full wavelength plates to augment standard polarization and so, I decided to check out this box of slides and, in the process, discovered several interesting things.

 In my previous article, I mentioned Orange G which is especially intriguing because of its wonderful crystals, the variety of colors, and the fact that it is birefringent through the entire rotation of the analyzer.  I discovered in my slide box, several preparations where I had mixed Orange G with some other stains and chemicals to see what sort of synergistic results I might get. Also I had not yet taken time to cut the compensators to the proper dimensions.  As a result, I was holding the compensator in the substage light path and noticed that when I accidentally tilted the compensator, the angle of tilt shifted the background color as does the angle of rotation.  I was using a full wavelength filter and I so liked the effect, that I decided to cut and mount one filter and leave the other unmounted to allow greater freedom of angular experimentation.
 My little bit of investigation thus far has led me to believe that the full wavelength filter is primarily useful in providing color contrast (which in some instances is stunning); the 1/4 wavelength filter seems to be most useful in providing an oblique pseudo-3D perspective on certain types of crystal faces.

 With most samples, I look at them first with regular polarized light and then with the full wavelength compensator which I rotate and tilt until I get the most desirable color contrast.  If the crystal faces show both angularity and depth, then I try the 1/4 wavelength compensator also.  In the list below, I am talking only about samples which are of interest under polarized light and, in some instances, with a compensator added.  Remember that some crystals may be of interest with bright field illumination, but not of special interest with polarization.

Preparations of Interest Under Polarized Light

1) Methyl Red
2) Copper sulfate
3) Aluminum ammonium sulfate crystallized and then stained with Orange G.
4) Marine phytoplankton in the old Turtox CMC-10 non-resinous mounting medium.  This produced some lovely bouquets of needle-like crystals which I  suspect were the result of the medium reacting either with the traces of marine salts or traces of the preservative or both.
5) Methylene Blue + Orange G
6) Copper acetate + Orange G.  This particular preparation didn't seem very interesting at first with a magnification of 100x; however, by increasing the  magnification to 250x and increasing the illumination slightly, I was able to observe some very beautiful small crystals.
7) Silver nitrate
8) Anbesol—a commercial product for cold sores and sore gums.
9) Rochelle salts (sodium potassium tartrate)
10) Magnesium sulfate + Orange G. (Spectacular!)
11) Trisodium phosphate
12) Mouthwash
13) Potassium phosphate (Very good)
14) Sodium bisulfite
15) Ferric ammonium sulfate (Spectacular with the full wavelength compensator)
16) Aluminum ammonium sulfate (this is another instance where the crystals are of  more interest at higher magnification.)
17) Inderal—This is the brand name of propanaolol, a blood pressure medication.  Very interesting crystals.
18) Toothache liquid
19) Ferric ammonium sulfate + Orange G (Very impressive)
20) Chlorox + Orange G
21) Ferrous ammonium sulfate (Wonderful)
22) Sodium bicarbonate (Baking soda)
23) Sodium bicarbonate + Sodium silicate (Very good) Sodium silicate used to be  used as an egg preservative and is still available in some drugstores.  It has a tendency to "crackle" when it dries and can produce some very interesting  results when combined with various salts.
24) Rochelle salts + Sodium silicate (Again, best viewed at about 250x)
25) Wart remover (This is a 10% solution of sodium salicylate)
26) Phenylephrine hydrochloride (Nose drops—very good)
27) Marine salts
28) Sodium bicarbonate + 4% Sodium silicate (Spectacular)
29) Sodium borate + Orange G (Very good)
30) Nickel sulfate + Orange G
31) Sodium thiosulfate
32) Manganese chloride
33) Vitamin C (Spectacular!!!)

 These are some of my successes, but there were many other samples which were failures.  One final suggestion: it's a good idea to keep records of your failures as well, so that if 2 years later, you want to make some slides, you can check and see whether or not your list includes something you were thinking of trying again. So keep trying out various substances and enjoy the fun of discovering which ones reveal some of their colorful secrets under polarized light.

 All comments to the author Comments to the author sent via our contacts page quoting page url plus : ('rhowey','')">Richard Howey are welcomed.
 

Microscopy UK Front Page
Micscape Magazine
Article Library


© Microscopy UK or their contributors.

Published in the March 2002 edition of Micscape Magazine.

Please report any Web problems or offer general comments to the Micscape Editor,
via the contact on current Micscape Index.

Micscape is the on-line monthly magazine of the Microscopy UK web
site at Microscopy-UK



© Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.