Dating sylvac marks
Note that glass is sometimes classified with ceramics (at the Victoria and Albert Museum, for instance).
Slip is liquid clay, and can be piped on like icing to make squiggly patterns (as in Hornsea slipware).
Very artistic, I'm sure, but presumably the vases are now covered in scratches and chips.
Other e Bay fetishes are to photograph the object on an unmade bed (were the sheets clean?
Crazing is a curse of ceramics colletors and indicates that the factory did not bother to adjust the thermal expansion coefficient of the glaze to fit that of the body. Decoration Decoration may be underglaze, in which case it is dishwasher proof.
Crazing lines can harbour bacteria, so crazed pieces should not be used in the kitchen or on the dining table. However, underglaze decoration is limited in scope because the colours have to be resistant to the heat of firing.