Satin white
Satin white , also called gloss white , is a white mineral suspension and is similar to the mineral ettringite . It was first produced in England in the 19th century as a coating color for coating paper made from alum and milk of lime .
- Al 2 (SO 4 ) 3 + 6Ca (OH) 2 + 26H 2 O = Ca 6 Al 2 [(OH) 12 | (SO 4 ) 3 ] · 26H 2 O
As a rule, satin white is adjusted to a pH of over 12.5 with an excess of about 1 mol of Ca (OH) 2 . The exothermic reaction produces a finely crystalline, bright white precipitate which is suspended with suitable dispersants such as polyacrylates or casein to form slurries with 30 to 50% ettringite solids.
Because the handling of the suspension was problematic due to its extreme stickiness and pH sensitivity (it already disintegrates at pH values below 9), it was also called "Satan's White" or "Devil's White" in the paper industry. However, it was indispensable for decades because it was one of the most effective white pigments for satined papers before the industrial production of titanium dioxide . Satin white was used to produce art paper with high gloss and high whiteness , which achieved its high quality through a special calendering process for an excellent print image and an exceptional feel . Papers are still manufactured using this process today, for example the “Gohrsmühle” brand from the Reflex paper mill , art paper from the Scheufelen paper mill and glossy paper in Asian paper mills.
Satin white has been increasingly replaced in recent decades by kaolin or calcium carbonate pigments that are also suitable , as well as by the ettringite pigment casul ( calcium aluminate sulfate ) produced using a new process .