The final varnish is the layer that each oil painting, sometimes after months and months of processing, receives last. It is applied after a long waiting period (up to one year from the completion of the work), only when all the painting in its thinnest layers (glazes), as well as in the "thicker" ones (impasto), is completely dry. Composed of a substance obtained mainly from natural resins, it is also called "sacrificial layer" obviously referring to the fact that it will be this last transparent veil that will take on all the aggressions that the painting will undergo over time by light, by sudden changes in temperature , humidity and dust, allowing the paint to remain intact.
But to this term associated with the last painting, an always exciting moment and not without objective difficulties and therefore requiring great attention for those who want to perform it correctly, thanks to the revitalization of all the colors, to the uniformization of any dried up areas (opaque areas) and to the luster it gives to painting, a higher meaning can very well be attributed, where one wishes to refer to its etymological meaning: from the Latin sacer - facere = to make sacred.
Here, a few years ago, while I "sacrifice" a copy of Judith and Holofernes by Caravaggio (1602).