1 INTRODUCTION

SINCE THE EARLY '70's, acrylic dispersions have been used increasingly as non-penetrating lining adhesives. Their ease of application and relatively low toxicity have contributed to their gain in popularity.

One acrylic dispersion that is used by conservators in the United States is Alois K. Diethelm's AG Lascaux 360 HV. In addition to the properties mentioned above, it comes in a form ready to use and has a low activation temperature.

Empirical use seemed to show that a wide range of bond strengths could be produced by varying the lining conditions, i.e., heat or solvent activation, pressure, “drying time,” sizing of materials. Quantitative experiments have confirmed some of the above.3,7

The purpose of this project was to measure and compare bond strengths obtained when lining under varied parameters, using Lascaux 360 HV as the adhesive. Bond strengths were measured by peel and lap/shear tests.

The lining parameters chosen were based on previous quantitative testing and empirical use of the adhesive in the lining of paintings. Quantitative tests of Lascaux 360 HV have shown that sizing the original canvas with Acryloid B-72 increases the strength of bonds.3 Furthermore, empirical use has indicated that sizing the lining canvas also affects the bonds strength. Another qualitative observation has indicated that the “drying time” of the adhesive influences bonding. It has seemed that the bonds produced, when lining with Lascaux soon after it was dry to the touch, are stronger than the bonds produced when allowing for a longer period of time between application and lining.

This experiment tested the influence of two lining parameters:

1. drying time of the lining adhesive;
2. sizing of materials.

First, peel and lap/shear results were compared between linings performed 1 hour and 24 hours after application of the adhesive. One hour was chosen because it seemed to be the approximate time it took for the adhesive to become translucent and not wet to the touch. Twenty-four hours was chosen because it was assumed to be long enough for the dispersion to lose most of its water. Also, based on personal observation, twenty-four hours is a reasonable length of time a conservator will wait between application of the adhesive and lining. Since the dry film of Lascaux 360 HV remains tacky, a longer waiting period would increase the possibility of having dirt clinging to the film.

Second, peel and lap/shear results were compared among linings where the original canvas was sized or unsized and/or the lining canvas was sized or unsized. The sizing material was Rohm and Haas Acryloid B-72.

When non-penetrating adhesives are used in the lining of paintings, these latter sometimes need to be consolidated in a separate procedure. The use of acrylic resins for this purpose has been mentioned.1,2,5,6 Mehra5 uses a 5 to 10% solution of Rohm and Haas Plexisol P-550 (polybutyl methacrylate). Two advantages of using an acrylic resin over a wax-resin mixture is that the acrylic resin will not darken even a thin paint film and retains some flexibility in the original canvas. In this experiment, Acryloid B-72 was chosen for its known stability and because it is sometimes used as a consolidant for paintings.