A comparison of fumed silica and precipitated silica as matting agents for acrylic paint

Elizabeth La Duc and Dr. Aaron Shugar

Abstract

The use of matte paint is often required in conservation for successful inpainting. A matte surface can be achieved in several ways, for example, by using a paint with a high pigment concentration, by abrading the surface to increase roughness, or by adding a matting agent to the paint. While fumed silica is often used as a matting agent by conservators, its efficacy has been called into question. Fumed silica is produced commercially as a thickening or thixotropic agent, not as a matting agent; in contrast, precipitated silica is sold specifically as a matting agent. Paint samples modified with fumed silica (CAB-O-SIL M-5, Cabot Corporation) and precipitated silica (ACEMATT HK 125, Evonik Degussa) were compared with gloss analysis, colorimetry, and differential scanning calorimetry (DSC). In addition, the characteristics of a commercially available matte acrylic emulsion paint were investigated. Precipitated silica was found to be easier to use than fumed silica and nearly as effective at reducing gloss, with a 1% addition to paint reducing gloss by over 60%. Commercially available matte paint was found to be glossier than expected or desired, reinforcing the importance of understanding and testing one’s materials.