I “accidentally” made resin swirl fins the first time I attempted to lay up fins and I was really happy with the way they came out. I will be posting pics soon b/c they ended up on a 6’1 fish that I shaped.
Basically, I took a sheet of glass about 12" X 12" and cut 6 oz cloth the size of the glass. In total, I think that I used about 15-20 pieces of cloth to make medium width keel fins. In retrospect, I probably would have used 4 oz cloth but 6 oz is what I had so…
Anyway, I then started laying up the fins with purple resin. I took 3 sheets of cloth, laid them on the glass and saturated them with the purple resin.
Next, while the purple was still wet (as in RIGHT after I saturated the first 3 sheets with purple resin) I laid down 3 more sheets, took another color - I think it was red - and completely saturated the second 3 sheets of cloth.
At this point, I saw that the purple was “bleeding” through to the red, which initially bummed me out because my intent was to make fins that had alternating colors so that when I foiled them I would end up with 2 keel fins that went from white-to-red-to-purple.
But the more I thought about it, the more I liked the way that the purple was bleeding through so I just went with it and continued the above process - adding 3 sheets of 6 oz. as soon as I saturated the preceding sheets of cloth and then completely saturating using a new color.
In total, I used purple, red, white, and pink. When I foiled the fins, they came out really cool - sort of a redish-white-pink marble effect with solid purple on the flat side of the fin.
I think that the key was setting the resin up really slow so that it didn’t kick before I had finished laying up all 15-20 sheets of cloth. Also, I really worked the resin in hard and “smooshed it down” to cause the resin from the preceding layer of cloth to bleed through.
Anyway, I hope that helps. There are probably better/easier ways to get the same result and hopefully some of the old timers will chime in, but that is what worked for me.
Pics coming soon.