MAKING PLASTIC REPLICAS OF SNOW CRYSTALS

The study of snow crystals under a microscope or making photomicrographs of their beautiful designs is a cold and painstaking task. However, a method developed some years ago by Dr. Vincent Schaefer of the General Electric Laboratory at Schenectedy greatly aids the microscopist in this endeavor. It is to make plastic casts of snow crystals on microscope slides. These slides may then be photographed more easily or even used for microprojection, a feat which would be impossible with real snow crystals.

Schaefer's method is to use a 1% solution of formvar 15-95, a polyvinyl formal resin, dissolved in ethylene dichloride. This solution must be chilled below freezing before using. The crystals are caught on a board covered with black cloth, and then a glass rod or wire dipped in the plastic solution is touched to likely looking specimens which are then transferred to a microscope slide. Another drop of solution is placed on the crystal on the slide, as shown in the photograph of Dr. Schaefer making a slide. The solvent evaporates quickly, leaving the flake encased in a shell of plastic resin. Later the water forming the snow crystal evaporates thru the plastic's pores. The thickness of the shell of the replica is estimated at around 20,000 angstrom units by Dr. Schaefer.

All of this work must be done, of course, out of doors or in a building at the same temperature as the outdoor air, and all materials used kept very cold. We have found in this section of the country (Iowa) that the best crystals fall during snowstorms when the temperature ranges between 10 degrees and 20 degrees F., and generally when the wind is northeast. Above 20 degrees the crystals melt more easily and do not always show the fine detail of the colder ones---they also tend to be more of the open or branched forms.

A couple of little gadgets we have found helpful in making snow crystal slides are a spacing guide and a scraper f or removing unwanted specimens. The guide is of black cardboard marked in 1/4" squares in white ink, the crystal slide being placed on it while making the replicas. A small scraper, about 3/16" wide, can be made of a bit of razor blade mounted on a matchstick---this will easily remove damaged or uninteresting replicas from your slides.

The plastic replica method described above was used by Dr. Schaefer in connection with research on precipitation static for the air force and also in his famous rainmaking experiments.

581344 6 SNOWFLAKE CASTS MADE BY VINCENT J. SCHAEFER OF Q-E RESEARCH LABORATORY. VIEW (ENLARGED 20 DIAMETERS) WITH BOTH REFLECTED AND TRANSMITTED LIGHT UNDER MICROSCOPE. FILING NO.8851, 551.57, 3-10-41

Illustrations from Bentley and Humphreys book, "Snow Crystals": This book, "Snow Crystals", by W. A. Bentley and W. J. Humphreys ( McGraw-Hill, 1931), contains photomicrographs of thousands of beautiful snow crystal specimens, made over a period of 50 years by W. A. Bentley of Jericho, Vermont. No two of the designs are alike, and often show a remarkable mathematical regularity in their forms. (Plate reproduced courtesy of the publishers and the United States Weather Bureau.)

(From General News Bureau. General Electric Company. Schenectady 5, N.Y.)

Plastic replicas of snowflakes being prepared on glass slide with technique developed by Dr. V. J. Schaefer, General Electric scientist. After snowflake is caught on slide, a single drop of plastic solution of Formvar is placed on snowflake. Solution dries, leaving hard plastic cast of perfect reproduction of snowflake.