Gloss Reconstruction in Modern and Contemporary Art: Perceptual Challenges and a Varnish-Based Retouching Method

This is a preprint submitted to Zenodo prior to peer review. Please do not cite without the author's permission until formal journal publication. This paper addresses the problem of angular gloss variability in the conservation of modern and contemporary paintings - a condition in which a paint surface exhibits different specular reflectance characteristics depending on the angle of observation. A localised retouching methodology is proposed, based on the controlled application of conservation varnishes at different gloss levels using adapted tratteggio and pointillist techniques. The optical interaction between varnishes of different specular reflectance, applied in fine strokes or dots, produces a perceptually averaged gloss level through a mechanism here termed the vibrating retouch effect, which contributes to visual integration across multiple viewing conditions simultaneously. A case study conducted at the Centro Conservazione e Restauro La Venaria Reale (Turin, 2023) on a painting by Gian Carozzi (Senza titolo, 1952, oil on canvas) illustrates the practical application and limitations of the method. Experimental validation through sample-based glossimetric analysis using five conservation varnishes (Regalrez 1094 at two concentrations, Laropal A81, MS2A/MS3, and Paraloid B-72) is currently in preparation.