Identical ink to the 50 ml: the same dark grey-violet, the same neutral pH, the same 14-second dry time on laid paper. What differs is the bottle. This one is round rather than faceted, with a tall narrow shoulder and a small flat well in the base, which means you can get a full fill out of the last 4 ml by tilting it — something the wide 50 ml bottle will not do.
30 ml is roughly twelve fills of a standard converter, or about four months of daily use in one pen. If you rotate between pens and inks, this is the right size; a 50 ml bottle of a colour you use occasionally will outlive its own freshness.
Same caution as the large bottle: it is a dye ink and it is not waterproof. For anything that must survive water, use the iron gall document ink instead.
