Microscope Activities, 25: Slide Ringing

In the past, Hooke College of Applied Sciences offered a microscopy workshop for middle school and high school science teachers. We thought that these basic microscope techniques would be of interest not only for science teachers, but also for homeschoolers and amateur microscopists. The activities were originally designed for a Boreal/Motic monocular microscope, but the Discussion and Task sections are transferable to most microscopes. You may complete these 36 activities in consecutive order as presented in the original classroom workshop, or skip around to those you find interesting or helpful. We hope you will find these online microscope activities valuable.

EXPERIMENT 25: Slide Ringing

Goal

To understand the construction, use, and purpose of a commercial slide-ringing turntable. Optionally, a simple slide-ringing turntable may be constructed from readily available materials, and used to ring various microscope slide preparations.

Level

Basic – Intermediate

Materials Needed

Commercial slide-ringing table, or one constructed from scrap wood, a ball-bearing, and a thick piece of plastic or metal; or discarded VCR; or discarded computer hard drive; common hand tools. Various slide ringing cements (see text below); paint brushes.

Procedure

Figure 25-1 illustrates two commercial slide-ringing turntables.

A microscope slide preparation with a round coverglass is placed on the brass table, and secured with the spring-clips (stage clips). The round coverglass is centered using the series of concentric rings scored into the surface of the table. Then, while the table is given a spin with the finger of one hand, the other hand, supported on the non-rotating part of the table, lowers a paint brush charged with, e.g. paint to the outside margin of the spinning coverglass, thereby applying a neat ring and sealing the mountant from exposure to the air. Using a commercial or homemade turntable, as will be described shortly, make a deep-cell slide preparation, or seal an aqueous mount, or prepare a “finder ring” as described in the Discussion.

Discussion

First of all, what is a slide-ringing turntable, and what is it used for? A slide-ringing turntable is a relatively simple device that allows one to spin a microscope slide about its center point, while applying liquid cement, paint, gold size, shellac, etc. with a paint brush to the margin of the coverglass. There are many reasons for wanting to do this, chief amongst which include:

1. Building-up cells for thick microscope specimens.
2. Sealing the edge around round coverglasses where aqueous mounting media, such as glycerin jelly or carboxymethyl cellulose solution have been used. The resulting seal both prevents the sample mount from drying out due to water loss, and from taking on water from saturated air.
3. Sealing Canada balsam or other resinous mounting media slide preparations after their solvents have been driven off, in order to prevent or retard darkening and discoloration due to oxidation over time.
4. Preparing a cell for liquid mounts.
5. Preparing “finder rings”: one (usually) or more very thin, tiny diameter rings are spun on a glass slide in the center of which one or a few tiny specimens are affixed before a mounting medium and coverglass are added, and then sealed; the “finder ring” helps to quickly locate the microscopic specimen(s).
6. Repair of damaged or brittle rings on older slides.
7. Color coding of specimens as to type, e.g. botanical (green), mineral (brown), etc.
8. Containment of pathogenic, radioactive, or volatile specimens.
9. Making petroleum jelly cells for live pondwater specimens to maintain coverglass seal and prevent or retard evaporation for making extended observations.
10. Ringing for pure aesthetics.

Construction of a Slide-Ringing Turntable

One of the older designs of turntables, described by Hogg in 1859 (1), is illustrated in Figure 25-2.

It consists of two circular wheels of wood imbedded into a solid block of wood, and secured there by central screws. A handle of wood is fixed to the top of one wheel to start and maintain a circular rotation, which is communicated to the other wheel by an endless bond of catgut running in the grooved edge of each. A similar device could be constructed today using pulleys. In addition to making rings of gold size, etc., the author suggests that round coverglasses can be made from square ones by lowering not a paint brush, but a diamond scriber onto a square coverglass [round coverglasses have always been more expensive than square ones; in 2009, an 18 mm round coverglass cost 17 cents vs 4 cents for an 18 mm square coverglass].

The slide-ringing turntable illustrated in Figure 25-3 was designed and made in 1959, and described in 1966 (2). It is constructed from scrap wood; the dimensions are not critical:

1. Base: 6” x 12” x ¾” (bottom covered with non-slip material).
2. Arm-Rest Support: 5¼” long, 1½” wide, 2½” high.
3. Arm Rest: 8” x 2½” x ½” (front edge set back 1/8” from center of table; the top is covered with felt).
4. Table Support: 5” x 3½” x 1¼” high (corner rounded; a hole is cut with a hole saw to accept an automotive ball-bearing with 2¼” outside diameter and 1” center hole).
5. Table: ¼” thick plastic, 5” diameter, with 1” diameter plastic dowel section 9/16” long is cemented in the bottom center so as to press-fit inside the ball-bearing.
6. Ball-Bearing: 2¼” outside diameter, 1” inside diameter, obtained from an auto parts store.

The 5” diameter stage is larger than on most slide ringers so as to accommodate double-mount slides. Two holes are drilled through the stage to accept ordinary stage clips. The center of the stage was found by rotation, and concentric rings were scribed around the center point in such a manner that their diameters correspond to the general range of commercial coverglasses (10, 12, 15, 18, 20, 22, and 25 mm).

One advantage of this design over others is that the arm rest overhang allows for the charged brush to be steadied against the leading edge of the arm rest and lowered slowly to ensure neat rings around the spinning coverglass. The large bearing makes for a stage that will coast for a long time with great precision and smoothness.

More recent homemade slide-ringing turntables have been made from a discarded VCR, and still another from a discarded computer hard drive! These are described both online, and in the microscopical literature.

Ringing Cements and Materials

The classic ringing materials include asphaltum (an asphalt-toluene mixture), japanners’ gold size, and proprietary products, such as Brown Cement. Asphaltum is not generally available today, but gold size is still available, although it may be hard to find. It is still used by traditional sign painters—the ones who still make the black and gold names on office door windows. It is also used by fine arts illustrators. In both cases, the gold used is genuine high-karat gold leaf. To make the gold leaf adhere to any surface gold size is applied to the surface; it is a kind of varnish that becomes tacky, at which point the gold leaf is applied with a special brush and then burnished.

A very suitable substitute for gold size for slide ringing today is shellac. Don’t buy any shellac; try to find the solid Orange Shellac Flake, and buy a can of denatured alcohol. Let the thin flakes of shellac dissolve in the alcohol, and adjust the thickness to paint consistency by adding either more alcohol or more flake shellac. The alcohol here should make this a good sealant where pathogens are being ringed. In the absence of solid flake shellac, you may try amber shellac that is already mixed with alcohols (Zinsser Co. Inc., or similar).

You may also use paint, but you do not want to use a paint that will harden and become brittle. The paints that are made for plastic models, and available in craft and hobby shops, work very well; be sure to buy extra solvent, because the paints, as supplied, are usually a bit too thick for slide ringing. Some of these paints and thinners can be seen in Figure 25-3, along with both clear and red fingernail polish, which may also be tried, but, again, somewhat diluted.

Collodion may be used, the kind with the camphor in it (“Flexible”); however, the combination of ethyl ether and alcohol solvent may be disagreeable.

Proprietary slide-ringing cements in clear, black, white, and gold (all thinned with toluene) can be purchased from Brunel Microscopes Ltd (www.brunelmicroscopes.co.uk); indeed, they also sell a ringing table with ball-bearing race and guide lines (~£21).

Brushes

Any good quality brushes made for use with watercolors will be suitable for slide ringing. Depending on the thickness of ring you want to make, the brush size may be anywhere from 0000 or smaller to up to 2; the nature and thickness of your ringing compound, and the width of your ring will inform you right away which brush size to use. You may want to use more than one size brush if you want to have multi-colored rings.

Technique and Results

Skill with the slide-ringing turntable will come quickly; the results will tell you if you are spinning the table too slowly or too fast; if your brush has too much or too little paint; if you are lowering the brush too much or not enough. Soon you will be on your way.

Figure 25-4 illustrates a number of possible paint color combinations [note also the square cover glass mounted in diamond configuration, which has had its four sides ruled with paint!].

Figure 25-5 shows a whole box of ringed slides. These are all primarily aesthetic, but you could choose to color code specimen type, or, as illustrated, you may wish to use colored adhesive dots to indicate specimen type (green=botanical; white=zoological; etc.).

Figure 25-6 (right) shows four microscope slide preparations in which the slide-ringing turntable has been used to make a “finder ring” (the small circle in the very center) is the center of which the specimen is mounted, prior to adding the mountant, the coverglass, and the final sealing ring.

Figure 25-6 (left) illustrates the use of the slide-ringing turntable to make opaque black backgrounds on which specimens are attached, prior to ringing of the coverglass.

Teacher’s Note: You may find several online suppliers for an inoculating turntable (Figure 25-7), which is a hand-operated turntable designed to produce concentric circles of evenly distributed bacterial colonies from the edge of a Petri dish to the center. There are two models: a 4½” diameter by 3” height (11 x 8 cm) for 100 mm Petri dishes, and a 6” diameter by 1¼” height (15 x 3 cm) for 100 mm and 150 mm Petri dishes. Either of these, if available, is easily converted to a slide-ringing turntable by drilling a couple of holes to accommodate stage clips, and, using a carbide or diamond scriber, scoring a series of concentric rings from 10 mm to 25 mm to act as coverglass centering guides.

Cited References

1) Hogg, Jabez (1859). The Microscope: Its History, Construction, and Application.

2) Delly, John Gustav (1966). A New Slide-Ringing Turntable. Microscopy: Journal of the Quekett Microscopical Club 30 203-205.

For German readers there is also:

Hevers, Jürgen (1986). Eine Drehscheibe für Lackringe. Winke fürs Labor. Mikrokosmos 75 Heft 8, 248-249.