Golden Open Acrylic 

GOLDEN OPEN Acrylics are a slow-drying formulation with a slightly softer consistency than Golden Heavy Body paints. The increased working time of these colors expands their range to include more traditional techniques once only possible with oils.
Because OPEN Acrylics dry slowly, painters who cover their palettes or use sealed containers have been able to use the same colors for weeks, reducing the amount of paint wasted and preserving color mixtures for future use.
OPEN Acrylics resist skinning on the palette during long painting sessions and when painting outdoors. Thin applications of paint tack-up, allowing additional layers to be applied and blended. Thicker applications may be worked for hours, however paint over 1/16" thick will dry EXTREMELY slowly.