Potlids are a staple of 19th-century pharmaceutical antiques, with the most common, in my experience, being toothpaste containers. Some time ago, I was lucky enough to find a fragment of a lid while mud larking that still had some of the text on it.
I guessed from the word "Enamel" that it must've been from a toothpaste pot, but I didn't look into it any further until I came upon the full version of the very same lid in an antique shop and recognised it from my fragment.
It's a particularly fine example, with only a slight crack on the left-hand side and free of any chipping. Although the rest of the lids in my collection have broken rims and evidence of repair, this one is nearly perfect.
W. Woods & Son was a Plymouth-based chemist that operated, as far as I can tell, throughout the 19th century and into the 20th. But according to "Antique Bottles Collectors Encyclopaedia", their pot lids get found all over the globe. This could be because they were exported, or people visiting other countries brought their toothpaste. I imagine it to be both.
Other toothpaste, such as cherry flavour, existed, but areca nut seems to have been the favoured ingredient. The areca or betel nut was used in Arabia prior to its introduction to Britain in the 1800s. Traditionally, the nut is chewed to promote the strength of teeth and gums, though it leaves a blackish pigment in its wake. To counteract the staining, English pharmacists included betel nut charcoal in their toothpaste, though this rendered the actual benefits of the nut useless. So whether the areca nut toothpaste was effective at all is doubtful.
(More on the usage of betel nut in toothpaste can be found in "Journal of the History of Medicine: Vol. 39, January 1984, Toothpastes Containing Betel Nut (Arec a catech u L. ) from England of the Nineteenth Century" By Peter A. Reichart - where I got my information for this post)
Pot lids are a varied area of antique collecting, which I find particularly interesting as they encompass a day-to-day aspect of 19th-century life. They were items that would be kept in the house and considered ordinary, but thanks to the text that remains on them, a lot of history can be teased out of a small piece of ceramic.