or

When zinc oxide is heated with cobalt nitrate solution, a green coloured mass of cobalt zincate is obtained called Riemann's green. You can also see it in class 11chemistry lab practical of basic radical identification ( Filter Ash Test) .

If the salt solution contain Zn², then filter Ash Test shows green colored mass which is Riemann's Green.

Riemann's green is a green pigment ZnO.CoO, which is obtained by heating a mixture of zinc oxide and cobalt nitrate or by the reaction of cobalt nitrate with either  or zinc sulphate.