1. Find out the contraction of your impression materials.
All impression material contract or shrink to their greatest mass, making the size of the imprint slightly larger than the original object.
2. Use a reported low expansion Die Stone.
Matching the expansion of the stone to the contraction of the impression material may make the resulting model large.
3. If the “fits are tight”, use a larger expanding Die Stone.
The fit of the coping/crown over the prepared surface or die.
4. Not all Doctors perceive “tight” the same.
Find out exactly where the tightness occurs before changing your process.
5. Surface problems with the stone are not Chemistry IN the stone, but Chemistry acting ON the stone.
Make sure that the impression is free from all contaminants, both biological and chemical, before pouring.
6. Use low expansion Base Stone.
Mid or high expansion stones may cause die drift showing as ill-fitting bridges or contacts.Don’t solve one problem, only to cause another.
7. When switching stones for other working properties, use the same or close expansion.
8. Higher compressive numbers do not necessarily equal HARDER surface.
The reported numbers are a factor of compression, not hardness. No one reports Brinell or Vickers numbers relative to surface hardness.
9. Combining stones changes all the properties.
Some users make up their own "Specialty Stones". These non-homogeneous mixes will change all of the corresponding physical properties numbers, and expand or set differently in each part of the mix.