What an amazing project,
@Aries M ! It reminds me of religious icons like found in the orthodox christian traditions. I have seen many icons in churches in Crete that involved backgrounds of gold leaf with lettering / calligraphy on top of it. That is very different from the technique of first applying the gold base like done in Western christian manuscripts for initials (like others said). But this is usually done for one, often big and elaborate initial, not for bigger amounts of text. I don’t know how the calligraphy is applied on the gold in the case of the Greek or Russian icons, but I am pretty sure it is done
after laying the gold.
In the German section about icons on Wikipedia I also found this technical order: 1) Choosing and preparing the wood, 2) Applying a base on the wood so that it can take colour and / or gold leaf, 3) Drawing of the outlines, 4) Gilding of the parts that should be gold, 5) Painting of the icon, 5) Applying of details etc.,
lettering on gold or colour, 6) Varnishing the icon.
There were more steps involved, but that is the basic sequence. There are still today icons made in the traditional technique. Sadly, I don’t know and a quick search hasn’t told me
how the lettering on gold is done exactly. I suspect oil or tempera paint with a brush (so that the gold is not destroyed with a hard writing tool).
I guess getting in touch with a Greek or other Orthodox icon painter would answer this fascinating question best …
I found this lady on IG:
https://instagram.com/greekiconographer?utm_medium=copy_linkShe has some examples of writing on gold, and she mentions using egg tempera. Maybe scroll through her feed to find out something!