Burnt Goose is goose nashua (flank) feathers that have been burned with a weak bleach and water solution to remove some of the feather web. Most of the so-called burnt goose that is available commercially has not been burnt by the bleach and water. It is dyed white goose nashua (flank) feathers and it is left to the tyer to bleach them to make them useful.
Burnt goose makes a very nice spey feather; however, keep in mind that the stem of the goose feather is rather thick and as such is very prone to splitting as you wind the feather. To make the goose feather supple you have to soak it in water with some hair conditioner added to it. Then when dry, it remains supple and the stem doesn't split when wound.