Varnish Is a Sacrificial Layer, Not a Finish

Six to twelve months for an oil painting, and longer for thick passages. The drying rung's point exactly: the film is still oxidising, still contracting, and still giving off small volatile products long after it is touch-dry. Varnish applied over paint that is still moving traps those volatiles, bonds into the surface, and cannot later be removed cleanly. It also cracks with the layer beneath, because the varnish sets long before the paint stops moving. Where a painting must be presented sooner, a RETOUCHING varnish is the answer: a much thinner, more permeable, deliberately temporary layer that evens the gloss and is replaced by a proper varnish later.

The conservator's requirement is that the varnish dissolves in a solvent that does NOT dissolve the paint. Natural resins like dammar and mastic satisfy that: they come off with mild solvents that leave a cured oil film alone. Their weakness is that they yellow and grow less soluble with age — an old dammar varnish needs stronger solvents than a fresh one, which is why very old varnish removal is difficult and skilled work. Modern synthetic varnishes based on low-molecular-weight resins were developed for exactly this: they stay soluble in mild solvents and yellow far less. Acrylic-based varnishes vary, and some cross-link over time into something that cannot be removed at all.

Two thin coats beat one thick one. A thick varnish layer traps solvent, stays soft, collects dust and is much harder to remove evenly later. Work in a warm room with low humidity. Varnishing in damp conditions causes BLOOM — a milky haze from moisture trapped as the solvent evaporates and chills the surface. It is a real and common fault and it is entirely environmental. Lay it on in one direction with a wide soft brush and leave it. Going back over a partly-set varnish drags it into ridges that cannot be brushed out, because the solvent has already begun to leave.

Write the varnish type and the date on the stretcher or the back of the panel. Whoever cleans the painting in fifty years needs to know what they are dissolving, and the alternative is testing on a corner of the work itself. Record the ground, the medium and any unusual materials too. A label saying 'acrylic ground, oil paint with stand oil medium, dammar varnish, 2026' takes a minute and is worth a great deal to anyone who has to intervene later. That is the notebook rung pointed forward instead of backward. Every other rung in this batch is about making the object last; this is about making the information last with it.