For the past couple of years,  my tap water has been curdling my paints.

It all started with a tube of Quinacridone Rust (PO48)  from M. Graham.   I was attracted to this paint partially because the pigment is listed as non-granulating,  and I fell in love with the colour, but ever since I got it, the paint has had a tendency to clump and curdle when mixed with water in the palette or dropped into a wash, resulting in an incredibly pronounced granulation pattern.  This pattern becomes even more pronounced when Quin. Rust is mixed with another dark valued, non granulating paint such as a phthalo.

Colour mixing experiments with Quin Rust (PO48) and Phthalo Turquoise (PB16)

I searched the internet extensively, and could find no other reports of quinacridone rust granulating like this.  For months I was actually convinced I had received a dud tube, but avoided investigating…