5 CONCLUSION

IT APPEARS THAT in general, sizing of the materials affects the bond strength more significantly than drying time of the adhesive. The strongest bonds were produced when both canvases were sized and the weakest bonds were obtained when the original canvas was unsized. When one component was unsized, bond strengths recorded between .08 and .14 Kg/cm which hovers around the lowest figure offered by Phenix and Hedley7 as a minimum acceptable value for lining (.12 Kg/cm).

It is important to stress here that the intent of this study was not to recommend the use of the products tested. Its only aim was to serve as guidance for conservators who use similar materials and methods. Also, because of the complexity of the variables involved during lining procedures, the results should not be analyzed in terms of specific numbers but rather in terms of general trends. In subsequent unpublished testing, the lining procedure was improved by using Dartek instead of mylar as a covering membrane. It was felt that a more even vacuum could be obtained with Dartek because of its “self-sealing” properties. Also, more accurate pressure readings were taken from the top, using a spot magnehelic gauge.

Another aspect which would have to be reconsidered in subsequent testing is the use of B-72 dissolved in xylene, as impregnating resin. Personal observation seems to indicate that the evaporation of the xylene from the canvas is much slower than one would suspect. Even though the linings were executed at least 10 days after impregnation, the samples still had strong xylene smell long after lining. It is possible that the increase in bond strength with sized samples may be partly due to the action of xylene still present in the system. Mehra5,6 recommends the use of Plexisol P-550 as consolidant; since this latter is soluble in weaker and faster evaporating solvents, its choice might be better as an impregnating resin.

As a last note, quantitative aging tests are not known to have been performed specifically on Lascaux 360 HV. However, Plextol D360 which is believed to be the base resin for Lascaux 360 HV has been tested by E. De Witte et al.8 It is obvious that more thorough aging tests should be executed before the product can be safely recommended. Along this line, our samples have all been peeled half way and we hope to take new readings after at least one year of natural aging.

ACKNOWLEDGEMENTS

DR. WALTER COBBS for permission to use the Nordson facilities; Mr. William Rehman who provided the data and significant help in carrying out the experiment.

Yucel Birol, Graduate Assistant and Dr. Gerhard E. Welsch, Director of the Central Mechanical Testing Facility at Case Western Reserve University for their investigation into the effects of cross head speeds in the evaluation of peel and lap/shear strengths of adhesives.

The Mellon Foundation, National Endowment for the Arts and ICA for their partial funding and Peggy Salo for word processing.