I've been making Ultracal-30 molds for many years (about 24) and what I found really works well is...
* Spray 2-3 layers of Crystal Clear Acrylic Spray on your Sculpt (WED or Chavant or Roma Plastalina or Clay of your choice)
(Allow each Layer to dry really well so it's dry to the touch BEFORE putting on the next layer...)
* THEN follow up with a layer of Dulling Spray on TOP of the Crystal Clear Acrylic Spray,
this may seem like a lot of trouble but not only does it work well but it makes clean-up even easier!