A low molecular weight varnish will tend to have greater gloss, higher refractive index and will provide greater saturation into the surface, due to the smaller molecular size, than high molecular weight varnishes. On the other hand, HMW varnishes tend to offer a better protective surface, have greater elasticity and more resistance to blooming. Although some new work by Ren de la Rie, Head of Scientific Research of the National Gallery of Art, has suggested various alternatives, we continue to prefer the polybutylacrylate systems, Golden MSA Varnish, which have so far proven the most durable and lightfast, and maintain their removability. Our other varnish, Golden Polymer Varnish, is unique in that it offers a water-borne varnish which meets the criteria of remaining removable and having good visual properties, while freeing the user from hazardous solvent exposure. In terms of film toughness and permeability, this varnish provides an intermediate level of performance compared to the MSA Varnish.
Rigid supports allow the use of much harder varnishes.
This is especially important when applications involve functional use of the artwork, as in furniture or floor designs. Often the varnish of choice in these applications is a polyurethane because they provide some of the most non-porous and toughest films available. They often fail the rule of a removable coating, but this may have to be accepted, depending on the application. Polyurethanes which have been available the longest, the aromatic type, are prone to yellowing. However, recent innovations have provided polyurethanes that do not yellow.