Tom,
I think most use a gravity-feed because they have to spray at a really low pressure to not blow the frosting off the cake.
Just remember that the airbrush should be one used for cakes only with nothing more than food coloring sprayed through it.
You don't want to use enamels and clean it with lacquer and then go spraying food coloring onto cakes with it.
I think something like the Omni 4000 or 5000 would be nice for that.
If you want to know more then send Ken an email and ask him.
His email is kenbadger@aol.com
Mike
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon