I would disagree that the swirl comes from method, not temperature. The swirl pattern is critically dependent on the amount of curing which has occurred prior to the colors being mixed. Too early and red with blue swirls turns into homogenous purple and too late, there will be bubbles. The curing reaction is exothermic, the mixture warms as a function of time as it cures. The trick is to find that Goldilocks moment where the colors are viscous enough to swirl without mixing, but not too late. This moment can be determined objectively by temperature. Granted, here temperature is a surrogate measure of viscosity which is much harder to measure accurately (at least by me, others are very good at it and have no need to use temperature)
The swirl has nothing to do with the amount of gelling, but in the procedure in which the colors are introduced. As the resin begins to gel, it becomes harder to get a swirl. The pattern becomes very distinctive color separations.
The mixture doesn't warm as a function of time, it begins it's exothermic reaction as a result of cross-linking. The larger the mass of the cast, the higher the exothermic output.
With this particular
Urethane resin, the open time is 12 minutes. Some urethane's are a little longer, some shorter.
In 12 minutes, it can be difficult to get the two parts mixed thoroughly, poured, and under pressure before it begins the gel. With a swirl, there are at least two colors to utilize in this process. This reduces the amount of time to get under pressure. Pressure is highly recommended when using urethane's. 12 minutes doesn't leave much time to linger, trying to test temperatures.
This is where the method plays a large role.
Of course, if using polyester resin, there is more open time, and is a completely different process.
I have never used Alumilite products, but all of the other
Urethane resins I have used, it is poured immediately after mixing all of the individual colors.
With polyester, the colors are mixed, and then relaxed for 5 minutes to eliminate the majority of the air inclusions, then poured. During the pouring, any remaining air is floated to the top of the mold.
The swirl will come from the method, not from the temperature.
But, do whatever works for you.
