Egg yolk(Egy) is yolk from a henn's egg. It can act as binder for pigments.
The characteristics of egg tempera are very unique. It requires a different technique than gouache or oil. 'Brush load' -meaning the amount of paint suspended in the brush when going from the recipient to the painting,is an important aspect of developing feel for the handling of tempera. It requires premeditated and accurate handling and is therefore less suited for expressive gesture. The finished look is incomparable to any other medium. The resulting paintwork is very brittle and must therefore be covered with some type of varnish for protection.
Egg yolk has been used as a binder since the earliest times.