What sublimation can and can't do
Imprint cotton shirts. Sublimation needs polyester in order to complete the process of transfer. Sublimation will turn out best with only 100% polyester shirts. Cotton shirts should be completed with heat transfer paper.
Imprint 65/35 and 50/50 shirts with bright colors. Since a percentage of the shirt is still cotton, the sublimation ink does not have enough polyester to create a vivid transfer. The image will end up with dull colors, especially after washing. Again, using heat transfers for cotton shirts is really the best option.
Imprint colored shirts. Any colored background drastically alters the imprint colors. Since sublimation will become part of the shirt, any color already on the garment will overwhelm the transferred image.
Imprint non-polymer-coated items. Remember that sublimation is printing into the coating, not the item.
Imprint gold/silver metal used by award companies. This is another instance where the background color of the substrate will interfere with the image.