<prompt> Greening refers to:Greenish discolouration of porcelain due to escaping of silver vapoursAlso known as wet strength of gypsum productObserved in silica bonded investments due to drying of colloidal silica gelAll of the above  <response>: Discoloration of the porcelain near the cervical region of the metal-ceramic prosthesis has been reported to occur when a silver-containing alloy is used as the substrate. Color changes included green, yellow-green, yellow-orange, orange and brown hues. This discoloration phenomenon has generally been called greening.Ref: Phillips Science of Dental Materials ed 12 pg 380 