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Peel Preparation Box: NOTES
The use of an internally illuminated wooden box with a plate glass top for making acetate peels is described. The plate glass provides a uniformly smooth, flat surface which inhibits air bubble formation even with relatively large specimens. A mirror on the bottom of the box is used to immediately observe the quality of the peel.
The technique of making peels of etched surfaces of rocks and fossils reviewed by McCrone (1963), Stewart and Taylor (1965), and Muller (1967), for example, has had profound effect on many sedimentological and paleontological studies. This technique has been improved to the point where many closely spaced serial peels can be made in a relatively short time at low cost with little wastage of specimens (Honjo, 1963). In many cases peels can be effectively used instead of thin-sections, which are costly, time-consuming, and more difficult to make. Liquid plastic can be used (Easton, 1942; Bissell, 1957; Stewart and Taylor, 1965), but most carbonate petrologists and paleontologists favor applying a thin sheet of cellulose acetate (Lane, 1962; McCrone, 1963) over the acetone-soaked, etched surface which is faced up (Lane, 1962; McCrone, 1963; Honjo, 1963; Stewart and Taylor, 1965; Muller, 1967; Davies and Till, 1968). Many of the difficulties encountered in peel preparation can be overcome with experience and practice, but fractured and porous specimens tend to produce air bubbles in peels unless they are first impregnated with plastic. However, unfractured and essentially non-porous medium to small specimens (1 or 2 cm in diameter) are difficult to handle, especially if they are relatively thin, unless they too are first imbedded in plastic.
Making acetate peels of medium to small specimens is easier if the etched surface is dipped in acetone, turned face down, and applied to the acetate sheet which is on a smooth, hard surface (Sternberg and Belding, 1942). Boardman and Utgaard (1964) used this method with thick (0.15 cm) acetate sheets which were previously sawed to the dimensions of a glass slide for easy handling and storage. I prefer this method but use thin acetate (about 0.01 cm) with a matte finish on one side (Lane, 1962; McCrone, 1963) because it is inexpensive and can be easily trimmed and slipped inbetween two glass slides or lantern slide glasses (McCrone, 1963; Muller, 1967) held together with frosted cellophane tape for protection, maximum flatness, and convenient labelling and storage. Howeve , this modification has two significant drawbacks: (1) air bubbles frequently occur even if the specimen has been impregnated with plastic and (2) one cannot immediately observe the quality of the peel without smearing it.
A simple solution to these problems is to work on a very flat, hard, transparent surface. I use a very cheaply constructed wooden "peel preparation box" with a plate glass top, a "five-and-dime store" mirror lying flat on the bottom, and one or two pairs of four watt fluorescent bulbs lining the bottom on opposite sides to illuminate the underside of the peel (fig. 1).
The procedure for making a peel with this box is as follows: Apply one edge of the acetone-soaked, etched surface to the matte finish of a slightly larger piece of thin acetate, then carefully rotate the specimen fairly rapidly until it is flat against the acetate and immediately release it. No pressure is applied, except for the weight of the specimen itself. If the peel contains air spaces, they can be readily observed through the mirror, indicating that another peel should be attempted. If the peel is good, free it from the plate glass after a few minutes with gentle pressure, using the sharp edge of a safety razor blade if it is stuck, and store it for about 24 hours to be sure it has enough time to dry thoroughly. Removing the peel after 15 (McCrone, 1963), 20 (Stewart and Taylor 1965) or even 40 minutes (Katz and Friedman, 1965) often results in stretching and wrinkling of the still wet, though apparently dry, peel so that it cannot be mounted in a perfectly flat position for microscopic study.
I have had few bad peels using this apparatus, even with specimens 58 cm in cross-section, because the plate glass insures a uniformly smooth and flat surface parallel to the etched
surface of the specimen under study. In addition, this method is faster, simpler, and easier than that described by McCrone (1963) and others. Any air bubble problems arise primarily from dust on the glass which is easy to clean, insufficient acetone on the specimen, and porous or cracked specimens that have not been previously impregnated. It has been pointed out to me that there is a risk of destroying very delicate structures, such as in the walls of fusulinids, by the rotation of the specimen onto the acetate and the slight pressure resulting from the weight of the specimen on the acetate. However, this procedure for making acetate peels of medium to small pieces of limestone and fossils is more than adequate for most paleontological and carbonate petrological needs (e.g., see Boa dman and Utgaard, 1964).
FIG. 1. Peel preparation box: Note the wooden frame, plate glass top, mirror on the bottom of the inside, and the 4 watt fluorescent bulbs lining the opposite sides of the bottom inside. The open end can be closed with a hinged door, and a frame can be firmly attached to the top to fix the plate glass.
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