Pour the resin for its intended use and leave the resin unprotected to dry in the air. The air's natural supply of carbon dioxide will cause the resin to carbonate. Resin carbonation repellants have special carbon dioxide resistant properties that block out the carbon dioxide so that it can't form carbonation, but leaving the resin out in the open, unprotected, is an effective way to stimulate the blushing effect.
Add more water to the resin mixture when you are creating it. Water contains higher levels of carbon dioxide than the air in the atmosphere. Because of this, more water leads to more carbon dioxide, or blushing, of the resin.
Aim a direct fire heater toward the resin to make carbonation appear. A direct fire heater, namely one that runs on gas, contains a high amount of carbon dioxide, which can expedite resin carbonation and increase the volume of it in the resin. Set the heater 2 feet away and leave it on for 30 minutes to see results.
Avoid using anti-carbonation protective coatings on the resin, which are designed to keep resin free of carbonation.