AIC's 43rd Annual Meeting

The goal of the CCI Lining Project, undertaken in phases since 1983, has been to understand the balance between the stresses in a lining and the stresses in the oil painting it presumably supports, as well as to observe and understand the ability of the lining to reduce cupping and cracking. In the early 80’s, new materials and new techniques emerged to address the disadvantages of previous structural treatments. At this time, we asked ourselves “Are these materials doing what we think they are doing?” Can a fabric lining dominate stiffness in a lining/painting composite, can it prevent cracking during fast events such as shock, can it help during daily and seasonal RH and temperature changes, and will it continue to support the painting for many years? We have reported data and conclusions as they emerged since 1987. All results have been placed in the context of standard viscoelastic polymer mechanics. In the final phase of testing (2011-2014), a completely redesigned stress relaxation measuring apparatus was used, much more precise and automated than the first system. Samples included an unlined model oil painting and linings on linen, multifilament polyester and sailcloth, using a flocked Beva 371 nap-bond adhesive and an impregnating wax-resin adhesive. A small initial strain was applied to the samples and stress monitored over several days. Five climate conditions were tested: 21⁰C/50%RH, 21⁰C/10%RH, 5⁰C/50%RH, -10⁰C/50%RH, 35⁰C/50%RH. These data were combined with the earlier 16 year room temperature data to build master curves of the stress relaxation over a range from milliseconds (relevant to shock and vibration) to decades. Measurements were also made of the response of lined paintings to rapid RH changes of ±10%RH and ±20%RH, held for periods of 1 hour, 4 hours, and 12 hours. This paper will focus on the main conclusions from the conservator’s point of view and will discuss the data in terms of the implications for the effectiveness of linings, both past and future. Of the linings tested the sailcloth was the only one to provide significant support and it will maintain this support over many years. A sailcloth lining will prevent overstretching of the painting during initial stretching and provides support at cold temperatures and during shock and vibration. In periods of low RH, however, the sailcloth contributes proportionally less support to the painting. Wax-resin linings provide significant support during initial stretching and during shock and vibration, but the support does not continue over the long term. Wax-resin linings reduce the response of the painting to RH fluctuations. Single layers of linen or multifilament, woven polyester do not provide support to the painting as they are never as stiff as the paint and ground layers. The value of the data in building our understanding of the role of RH and temperature in the cracking of paintings in general will also be briefly summarized.