I pour them both at the same time, but i let them get close to gelling first. i mix using PR (Silmar 41) and about 10 drops per ounce of Mek. I know that is prolly too much Mek, but they give it to me free with the PR, and i have had no problems with my blanks hardness or brittleness or anything so why change. plus, i have it mapped out with 10 drops. you got about 6 or 8 minutes of stirring. when it just starts to thicken, POUR POUR POUR. It is tricky, the closer you can get it to gelling, the better the seperation will be, but if you go too far, it will be too far gone and mess everything up. I got one mix so close, by the time i got around to the stopper mold, it was too far gone and the PR was all over the mold, the table, everything.
when i pour and it is still too wet, the colors become one, with very little seperation. Just part of the fun i suppose. Hope this helps.