1 INTRODUCTION

Discussion surrounding the cleaning of varnishes on furniture has not yet been as intense as that surrounding the cleaning of varnishes on paintings. However, in the last two decades some furniture conservators sought to save old finishes as much as possible. They believe that the uncritical removal of old finishes often results in a piece of furniture looking far too new, with an appearance unrelated to its true age. Moreover, the removal of old finishes also destroys evidence concerning the technology and materials originally used to finish the object.

This new awareness does not mean that every degraded finish has to be accepted as is, but new techniques have been developed to retain as much as possible of the existing layers, while at the same time achieving an aesthetically pleasing result (Landrey 1990; Schoeler and Stoian 1994). Many of the aging phenomena of old finishes are caused by the instability of the natural materials originally used. For this reason new resins were tested to see if they could attain higher standards of stability. Other criteria are that they should dissolve in solvents of low toxicity and that applying or removing the resin should not affect the old varnishes underneath. Some synthetic materials fulfill these criteria better than natural materials traditionally used in furniture conservation. This article deals with such a material, a synthetic resin called Regalrez produced by Hercules that can be used as a new top varnish on furniture and as a means to saturate degraded varnishes.

Hercules manufactures chemical raw materials, including hydrocarbon resins. Around 1983, Hercules introduced four low molecular-weight (LMW) hydrocarbon resins: Regalrez 1018, 1085, 1094, and 1126 (see table 1). Two more were introduced in 1991, Regalrez 1128 and 1139. The first “1” in the code stands for 100% hydrogenated, and the last three numbers stand for the softening point (�C).

Regalrez is a copolymer of styrene and styrene derivatives. The first two grades contain monomers like alpha methyl styrene and vinyl toluene to lower the softening point; therefore, they might not be as stable as the higher grades (Smit 1999). The higher grades are pure copolymers. Hercules suggests using these resins as additions in plastics to improve properties such as gloss and sealing temperature. Because of their adhesive properties and UV stability, Regalrez resins are used on a large scale for the assembly of double glazing.

In conservation, Regalrez 1094 has been suggested as the main component for picture varnishes (Rie and McGlinchey 1990; Rie 1993). Its gloss, saturation, and refractive index are comparable with those of dammar and mastic varnishes (Whitten 1995b), but Regalrez 1094 is far more stable. To further improve its properties, the elastomer Kraton G1650 and hindered amine light stabilizer (HALS) Tinuvin 292 may be added. Without Kraton G1650, Regalrez 1094 is as brittle as dammar (Rie 1993). Tinuvin 292 inhibits photochemical degradation reactions, thus keeping Regalrez 1094 soluble over a longer period of time. Compatibility with aliphatic solvents of low aromaticity enables Regalrez to be safely used on top of more polar varnishes or retouches. The aliphatic solvents needed to dissolve Regalrez are less toxic than aromatics. Finally, Regalrez 1094 gives a high saturation to degraded synthetic and natural varnishes (Whitten 1995b). Despite its good properties, Regalrez has not yet been widely used in furniture conservation.

Yellowed and crazed top varnishes on furniture are often regarded as unsalvageable and are therefore removed. Nonetheless, furniture conservators have developed many different techniques for saturating old varnishes. They can partly be solved and reformed by powerful solvents, or they can be saturated with natural resins. Another common practice is to apply a new coat of wax and melt it in with a hot-air gun. Finally, furniture reviver, which is a mixture of linseed oil, turpentine, ethanol, and vinegar, can be used. Many of these methods are intrusive and irreversible, or they add unstable materials to the old varnish.