Well, I don't think you will have any problem using the SIG as a base under the Brodak colors. Look into Brodak dope and ask if they use a non tautening dope as the base for it. All of SIG's color dope is based on their Lite Coat low shrink dope. If the Brodak are not low or non shrink dope, just order in some Dave Brown Flex-All to add to the thinned colors when ready to spray. It is a plasticizer and will keep the dope from continuously shrinking. In the old days they just added some castor oil to thinned dope to do the same thing, and IO think that is what Flex-All is, going from a simple taste test with medicinal castor. Make up a few test panels and let each coat dry thoroughly and give adequate time to gas off a bit. Light sanding in between coats too held adhesion. This may take some extra time but at least you will know what you have and what will work. Keep the list posted on what you find out.
Type at you later,
Dan McEntee