I swirl by preparing a double batch.
2 x 54 lb batches. If you color by steeping in the oil, or by steeping the lye, then you are forced to go with 1 to 1 (one batch uncolored, one batch colored).
Keep the two mold blocks on a short platform, basically right on the floor.
Half of the uncolored into each of the two molds.
Next, the colored batch, pour from between waist high to chest high, to fill up the two molds. Wander your drop, and enough impact speed to penetrate all the way to the bottom, 12 inches deep.
I swirl with a cut-out paddle stick with switch-back curves, usually 7 by 5.
If you color with a last-added colorant rather, then it's easier!
You can pour your first uncolored batch half into each mold.
Then pour about half of the second batch, still uncolored, so say, now each of the two molds is 3/4 full.
Now add the colorant to the remainder of the 2nd batch. (Mix it in with your electric mixer.)
Do your remaining pour now, wander your pour, and top off each mold.
For this 2nd way, the ratio is 1:2 or 1:3 or 1:4, you pick (less color). Swirl now with the paddle stick in each mold with 5 by 7 switch-back curves. The pattern looks better this way over 1:1 methinks. Avoid the solid-color core.
I cut a swirled double-batch into logs and then into bars for visitors on mini-tours in our store Saturday. They got to see some of them before I looked. The logs came out nice. The bars came out nice.
