The same iron gall as the 50 ml — pale blue-grey on the page, oxidising to permanent near-black over 48 hours, genuinely waterproof once cured — in a 100 ml bottle with a flat ground pour lip. This is a stock bottle, not a filling bottle. The mouth is wide and shallow, which is wrong for dipping a nib and right for pouring into a 30 ml bottle through a funnel.
If you have settled on iron gall as your working ink, this is the cheaper way to hold it: it is about 30 per cent less per millilitre than the 50 ml bottles, and iron gall stores well in the dark in a full, sealed container. It stores badly half empty in sunlight, where oxidation continues in the bottle and throws a sediment.
Decant what you need, keep the bench bottle closed and dark, and the rest will still be good in three years. Supplied with a funnel. The same flushing discipline applies: every two weeks in a filled pen.
