How were white background Greek ceramics from the Geometric period made? What gave them the white background?

by MrMedievalist
MrMedievalist

I'm thinking particularly of this one: https://upload.wikimedia.org/wikipedia/commons/2/2a/3139_-Athens-Sto%C3%A0_of_Attalus_Museum-Geometric_wine_cooler-_Photo_by_Giovanni_Dall'Orto%2C_Nov_9_2009.jpg