REPAIR OF BROKEN COVERSLIPS
ON PAPER COVERED SLIDES.
by Brian Darnton, UK
Some would say that damaged old slides are better left alone, but sooner or later one reaches that stage when the risk of incurring serious or terminal damage becomes an acceptable option. The illustrations cover the renovation of an example donated by a collector from Northern Wales.
(Slide of 'Gizzard of Cricket' with broken coverslip)
Coverslip breakage is probably the most common damage to old slides, much of it dating to the good old days before parfocal objectives were introduced.
It may well be that the coverslip is actually more or less whole but it has become obscured by particles from the objects like spores that have become attached to the underside of the slip. Slides stored in damp inappropriate situations like lofts or garages may be engulfed in fungal growth. A common enemy of the would be conservator. Alternatively the objects may have become detached from the black background or they may have become severely tarnished by dust and require cleaning and remounting.
REMOVAL OF THE UPPER PAPER.
Usually there is a single rectangular paper on the upper surface of the slide which is entire except for a 16-19mm aperture for viewing.
(The wet tissue laid on slide for 15 minutes only)
A 4"X1" strip of kitchen towel tissue is cut from a roll.
This is laid over the slide and enough plain water is dripped onto it with a pipette so that it becomes thoroughly saturated but not overflowing with water. After 20 minutes the strip can be removed and the upper paper can be carefully removed. It will become at once apparent that the remains of the coverslip are more of less still stuck to the paper and that all the gum that was used had been water soluble. If the paper is reversed in a sink, a model paint brush and water can be used to brush off the slithers of glass and if it is turned over the brush can also be used to free the dirt that has built up on the surface.
Awkward stains may be removed by very dilute soapy water, but avoid solvents or the ink may disappear. Most of the ink used by Victorians was water fast or became water fast after a period of time. The whole cleaning process should only take a few minutes. Prolonged treatment would also loosen the lower paper. After rinsing, the paper rectangle may be carefully dried in a flat inverted position. It will be hopefully free of gum, glass and much of the dirt.
(The upper paper removed)
REPLACING THE COVERSLIP.
If the objects are clean and secure on the black patch, then a new coverslip may be applied. The most satisfactory method is to invert the paper inside a large box lid and spray with 3M Photo adhesive. When dry the coverslip of the correct dimensions can be laid in the creases left by the broken one and carefully the paper with slip attached can be replaced on the slide. This 3M product which is a contact adhesive, allows a small amount of adjustment if the placement is not precise enough. Dry mounts which are not subjected to very high power objectives are better provided with a thicker cover glass and anything less than Number 2 is to be avoided. A diamond pencil may be used to cut glass from a larger slip if necessary
IMPROVING THE OBJECTS.
If dry objects like foraminifera are loose, freshly made gum tragacanth may be used to secure them. To be authentic most of these displays used to conform to some sort of geometric pattern and it is as well to try to try and reproduce this. Broken objects can be replaced if one has a supply of any of these. A Number 1 art brush and a Number OOO art brush may be used for manipulation, remembering that a Number 1 may also be used to withdraw excess of fluid if it is first wiped on a paper towel.
The work must be gently dried before sealing avoiding excess heat as such. Objects like the gizzard that are embedded in something like gold size or even black paint rarely require treatment.
(Completed work with coverslip replaced)
CELLS FOR LIEBERKÜHN ILLUMINATION.
The very small black mounting area surrounded by an annulus of clear glass is an indication that the cells were designed to be viewed under Lieberkühn illumination and its a good idea to take this opportunity to clean it thoroughly with a tiny pad of tissue dampened in distilled water and held by forceps.
Calcareous remains that have become grey will respond to removal by a damp brush and several days in hydrogen peroxide. The objects can be replaced after the patch has been cleaned or repainted with NBS mat black paint Again the gum tragacanth that leaves little in the way of a smear is one of the best adhesives.
Old slides are becoming increasingly valuable items and renovation is a risky business. Experience should first be gained on examples that are beyond hope before more worthy slides are tackled with appropriate caution.
Gum tragacanth, 3M photo mount, distilled water, NBS black background paint, hydrogen peroxide, paper kitchen towel, art brushes No. 1 and 000.
Comments to the author Brian Darnton welcomed.
Visit Brian Darnton's home pages.
Related Micscape articles by the author.
The construction of a Victorian type dry mounted slide.
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Published in the March 2000 edition of Micscape Magazine.
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