BLUES.

Ultramarine is perfectly good, and every body that likes to use it may do so.

Prussian blue, equals ultramarine in encaustic, for all intents and purposes; there is no other blue required for crayons neither.

Smalt may be used, but I think it rather too gritty; its particles are too transparent for parts where a solid mass of colour is required. For crayons it does very well mixed with Prussian blue to bind it, both together make a beautiful colour, the grittiness of smalt will there be of advantage. This colour will not grow black fixed with wax as it does in oil.