20th

Another house.  No longer residential, there's something to like in the way its door & windows, enclosed in metal, match the shutters of the buildings it sits between, and there's a brutal charm in the hard-edged lines of its wall-hugging stoop, leading to a padlocked entry. Do the top shutters slide open horizontally? It looks like it.
The use of metal seems especially appropriate here. 413-421 20th Street appear on the E.B.Hyde Brooklyn map of 1903 as a complex of stables, along with the wooden house pictured above, but by 1915 the buildings are housing a cornice-making business, Craig & Brown Incorporated.  Not just any old small-time business either. In 1914, Craig & Brown were responsible for sheet metal work on the 39th Street municipal ferry building, & the work was described in detail in the splendidly named journal, Sanitary & Heated Age.  A year later, Sheet Metal lauded their copper sheathing work on the City Hall Elevated Station, "A Contract Requiring Seventeen Tons of Copper for Siding, Cornices, Gutters and Downspouts."  In 1921 George Brown & two other partners founded the Munson Roofing Tile Company, which operated at this address.  By the 40s, the buildings housed a paint company & today, I believe, General Coatings manufactures chemical & paint products.

The bottom picture - Google Earth in black & white



Update 9/30/15: South Slope News  reports on the 20th Street site today, with news that 415 20th Street is up for sale ($4,500,000), with TerraCRG as the broker. I spend far too much time trawling the murky waters of local commercial real estate listings, but I missed this one. From the Terra site:

The property is ideal as-is for manufacturing/warehousing or can be converted into office, art studio, restaurant, event space and other creative commercial uses. The M1-1 zoned property features 11,400 SF of ground floor space with an additional 3,650 SF of office and mezzanine space. There are two drive-in doors, one with access to the interior of the building and the other provides access to outdoor space. 
Over the last decade Greenwood Heights has seen new residential buildings, retail shops and restaurants open to satisfy the demand for the new residents and businesses in the neighborhood. The area went through a rezoning that resulted in a number of new residential developments while preserving the historic character of the neighborhood and while some parts of the neighborhood remain commercially zoned, these areas have transformed from primarily traditional industrial uses to more creative uses such as outdoor beer halls, offices and hotels.

Personally, I think we have more than enough beer halls in the vicinity, and who needs another hotel, what with plenty of them farther west, and a whole rash of them in Sunset Park?  I'd prefer another manufacturing business that offers skilled jobs to local residents, but who knows what will come in? It's not clear from the listing if the whole of the 413 - 21 property is up for sale, but it seems likely.