I am interviewed about the possibility of making vegan egg wash, and here is my answer :
Did you see the results from the Seminar of molecular gastronomy... about egg wash (June 2023)? It is here : https://icmpg.hub.inrae.fr/travaux-en-francais/seminaires
and here
Later
on (this was published in another report), I understood that in order
to make a golden appearance, you need (1) brilliancy and (2) yellow.
For brilliancy, any layer that would be very smooth can be used (proteins in water, for example, but also oil, etc.). And for yellow, you use some yellow color (egg yolk or food colorant).