Frog
An indentation within a brick which reduces weight.
The frog face of the brick is normally laid face up for maximum strength.
Frosting
Fine wrinkled finish caused during drying of paints based on tung oil, etc., which have not been properly heat treated, (see Gas checking).
Frottage
Frottage 
A texture pattern achieved by overlaying a wet coat of glaze with lining paper crumpled to provide creases and folded areas.
Fugitive
Description given when a rapid partial loss of colour is experienced when the original colour is exposed to light and weather.