22 



THE ART OF MAKING MICROSCOPE SLIDES 



Cements 



able, the very similar cement of Harting 

 1880 are the best. The marine glue here 

 specified bears no relation to the so-called 

 marine glue commonly sold today. The 

 old-style marine glue, which is essentially 

 a mixture of rubber (or gutta-percha) with 

 shellac is one of the most water-resistant 

 cements ever invented. This style of 

 marine glue can still be obtained from 

 suppliers of microscope-mounting acces- 

 sories in Europe but does not appear at 

 present to be on the market in the United 

 States. If it is unobtainable, and the 

 technician is unwilUng to make his own 

 supply, gold size is the next best sub- 

 stitute. This gold size must, however, be 

 of the old-fashioned kind specified for 

 microscope mounting and not one of the 

 new varnishes which are placed on the 

 market for the benefit of gilders. It should 

 perhaps be explained at this point that 

 gold size was the material used by the 

 early gilders to apply sheets of gold leaf 

 on large areas. It was partially polymer- 

 ized and partially oxidized linseed oil 

 mixed with small quantities of resin and 

 diluted with turpentine. To the old gilders 

 it had the advantage that it took a long 

 time to harden so that it retained a tacky 

 surface, to which the gold leaf could be 

 applied, over a long period. The advan- 

 tage of this material to the maker of 

 microscope slides is that both boiled 

 linseed oil and turpentine will selectively 

 "wet" glass — that is, they will displace a 

 fine film of water from the surface of the 

 glass. They can therefore be applied to 

 damp glass to which they will remain 

 adherent. Modern gilder's varnishes — 

 sometimes called gold size — have the 

 advantage to the modern gilder that they 

 remain tacky for any specified period; to 

 the microscope mounter they have the 

 disadvantage that they are made in the 

 interests of the gilder, not of the tech- 

 nician, and rarely contain ingredients 

 which will adhere to moist glass surfaces. 



The attachment of a cell with gold size 

 was described in Chapter 1 and need only 

 be briefly reiterated. The slide is placed 

 on a turntable (Fig. 7) and a ring of gold 

 size of about the width of the cell turned 

 on the center of the slide. The undersur- 

 face of the cell is given a thin coat of gold 



size and both the slide and the cell are 

 placed on one side until the varnished 

 surfaces have become tacky. An additional 

 thin coat of gold size is then applied either 

 to the cell, or to the slide, and the two 

 pressed together. Since, however, a water- 

 proof seal is required, the cell must be 

 pressed firmly against the slide until the 

 cement has hardened, either by laying a 

 heavy weight on top of the cell, or by 

 placing another slide on top and clamping 

 the two together. 



The attachment of a cell with marine 

 glue is an altogether different proposition. 

 If a solution of marine glue is used, a thick 

 ring is turned on the sUde and a thick 

 coat is applied to the underside of the cell. 

 Both cell and slide are then warmed (the 

 lowest step of the hot table shown in Fig. 

 8 may be employed) until all the solvent 

 has been driven off. The slide is then laid 

 on the upper shelf, which should be 

 heated above the melting point of marine 

 glue. The cell is placed on the now molten 

 ring of cement and maintained in constant 

 contact with it until its own coat of 

 cement has melted and fused with the 

 cement on the slide. The slide should next 

 be transferred to the second or third shelf 

 (which should be just below the melting 

 point of the cement) and a heavy weight 

 placed on top while the cement slowly 

 solidifies. After a few minutes at this 

 solidification temperature, the slide is re- 

 moved, still with the weight or clips in 

 position, and laid on one side to cool. 

 It is then turned upside down and in- 

 spected to make sure that no air bubbles 

 have been caught in the cement. 



If solid marine glue is used, chips must 

 be scraped from the block with a knife. 

 A layer of these chips is then placed on one 

 surface of the cell (which in this case must 

 be of tin or some other metal) and the cell 

 laid on the upper shelf of the hot table at a 

 temperature which will melt the cement. A 

 heated needle is used to remove as many 

 air bubbles as possible from the molten 

 cement and the glass slide is laid alongside 

 it on the hot table. The hot slide is then 

 pressed firmly to the molten cement on 

 the upper surface of the ring. As soon as 

 the ring is firmly pressed into place the 

 slide is inverted, placed on the second 



