When the decal is soaked in water it releases as a thin layer of gum takes up water.
On glass, ceramics and any smooth non-porous surface this gum should be enough to hold the decal. You can apply some gum Arabic to the object to get more adhesion. To get a really good fix on shiny surfaces a little alcohol applied to the surface and the wet decal applied onto this before it evaporates. Overnight the alcohol will slightly melt the decal to the surface. On absorbant surfaces such as wood, plaster etc. then follow the real turpentine method.
For this method substitutes for turpentine will not work.