Hmm… I haven’t attempted a resin swirl yet, will be soon, but therefore I am of no help too you.
But you wouldn’t happen to be based out of Toronto would you? I read about 5 surfboards awhile back in SBC surf and how you are a small outfit for lake surfers.
Remember that the first color that hits the foam is the one you are going to see. If you want a red base with a darker red swirrel, then you need to pour the darker red first, then the base red over top. Or, mix up the base red with the hardner. Mix up the darker red in a separate cup with its own hardener. Stir them both well. Pour SOME of the dark into the base red and just dip a stir stick into the mixture once or twice. Then pour over the board. I'm really bad at explaing this so maybe someone will pitch in and give you a better explanation...
It takes some practice to get cool looking abstracts.