TotalBoat Halcyon can only be applied to oil-based stains if they have dried completely. Most stain products have a resin material in them that will cure or harden to a tack-free state.
It is strongly advised to always test the compatibility of any stain products used with a varnish on a small sample piece before attempting it on the final project.
Apply stain to a small sample piece of wood, similar to that on the final project. Once the stain has cured on the sample, apply the Halcyon varnish, as directed. Apply a few coats, and allow 48 hours to cure. To test for adhesion issues on the sample piece, make a small ccross-hatch pattern with a razor blade, deep enough for the blade to cut through the varnish, similar to a tick-tac-toe game, but with the cuts only a few mm apart from each other, enough to dig through the varnish. Then take a piece of duct tape and press it firmly onto the cross-hatched area. Allow it to adhere for a minute, and rip the tape off. If it has removed any of the varnish, there is a compatibility problem or other adhesion issue. If the tape has no effect on the coating when it is removed, Halcyon is safe to use over the stain.