And here I thought (before I'd finished the thread) that I'd found a possible clue...Just tidying up some blasts from the past (including some very ancient ones), largely for the benefit of anyone searching the site for information.
That’s the sliding cover from an inkwell by the Sanford Manufacturing company of Chicago:
View attachment 2130729
https://www.worthpoint.com/worthopedia/pat-1885-smco-sanford-mfg-co-chicago-1928618002
And here I thought (before I'd finished the thread) that I'd found a possible clue...
Sommer & Mills Co., North Attleboro MA
But there's no arguing it's the ink bottle cover.
Funny how some trademarks can be so similar...
"What this country needs is a good 5¢Sanford marketed it as part of their ‘Universal Ink Stand’ and, in advertising, claimed it to be the only practical stand with a permanent cover that met the demand for a five or ten cent ink.