For Fort Apache: Write-Up on Brookfield's History

Brookfield was incorporated in 1864 as Bushwick Glass Co., a bottle manufacturing facility. They officially became Brookfield Glass Company, the true business, in 1898 but likely were using that exact name before they incorporated it as no one has seen one saying Bushwick, which was the factory.
Many of their older insulators are simply marked W. Brookfield, too. Much newer ones were embossed with just a B on them.

When they began making insulators is unknown, but from 1868 to 1882 Brookfield's address on insulators was in Manhattan at 55 Fulton Street.
1882 to 1889 saw them as this one, 45 Cliff Street.
1889 to 1893 saw them on 55 Fulton Street.
None of the addresses actually produced insulators, which were made at their site in Brooklyn.

They had their insulators made in 'shops', which is why there is usually a number at the top of the piece. A 3-man shop was paid by quantity, not by the hour, so marking it as theirs got them their pay.
I'm not sure right now why this one seems to have two shop numbers, but I'm going to ask some people I'd consider experts.

They opened another plant and began making insulators at it in 1906. In the early 1910s they shut down their first location. The second location is usually where they made their darkest-coloured insulators, including the aqua/tealy ones that are darker.

By 1921 they had stopped production. My guess is that their quality had become so poor that Hemingray surpassed them too far. Brookfield is a great collection for crude pieces.
These earlier dome-embossed ones typically have weak embossing.