Tempera - varnishing

After painting, the tempera was covered with varnish.
Since it strongly changed color under it, so already during the painting process the later color change was reckoned for and the appropriate tone was selected.
In this way, the varnish was not only to provide a protective coating for the painting, but also to form a certain color whole with it.
In order to isolate the tempera from the varnish, it was covered before varnishing with a solution of soft glue (preferably fish glue) or protein.
Initially, the protein even served as a stand-alone final varnish.
Until fast-drying varnishes were known, tempera was covered with oil with amber and exposed to sun and air to dry.
Later, when quick-drying oils (with lead glycine) began to be used, they were used instead of varnish. However, since oil with siccatives blackens the painting very strongly, it was necessary to insulate the painting layer from the varnish with glue.