What is a decal or transfer? These are either designs or letters that are printed on paper. The paper is a carrier paper with an ink consisting of frit or a glaze-like material.
When your ready to add the decal onto your glass piece you need to dampen it. Once dampened you can add it to your glass artwork.
After the decal has been added to the glass your piece is then rolled onto a cloth or towel to remove excess moisture and bubbles. You then dry your piece overnight.
After your glass art piece is dry then you can fire it in your kiln. After this step in the process your design is sealed to the glass surface.
Voilla! An instant art creation! (well not so instant if you read the above article)
Because decals are in such wide demand many companies carry them.