Use these glazes for DECORATIVE WARE ONLY. Crackle glazes are not dinnerware safe, or good for vases which are to hold water.
Most glaze is intended to seal the clay to make it water-tight. When a crackle glaze is used, that seal is "cracked" and the ware can leak. This difficulty can sometimes be overcome by using a crackle on the outside only, and a non-crackle on the inside.
Staining crackle glaze - In most crackle glazes, particularly opaques, the cracks are not readily apparent until they are stained. The stain may be of any colorant such as iron oxide, umber, sienna, colored/india ink etc., mixed with water and brushed or rubbed over the glaze. After the stain is applied, it is wiped off the surface but will remain in the cracks and visually delineate the crackle pattern. To get the full crackle effect, do not apply stain until the glaze has stopped crackling after a week or more.