Ten blacks.
Sumi ink is soot held in a binder: traditionally animal glue, in some modern bottled inks plant glue or synthetic resin, as several here use. The soot (pine, oil lamp or carbon black) sets the hue a black takes when it is thinned to grey; the binder sets how it flows and how it layers. Every bottle of the year is registered by maker and product, and every painting with the inks it used. The papers.
When each ink was on the table.
The year began on three inks, used together until 8 April, then changed to a new set of three with the new papers. Later inks joined that set rather than replacing it.
Photo days, ink by ink.
Each dot is a photo day, sized by how many paintings used that ink. A painting made with several inks appears in each of their rows.
What each ink is.
From the maker's label and Peter's records. Binder and soot decide how a black behaves; where they are not known, they are left unknown.