Hundreds of brass hooks and eyes have been found on many American east coast archeological sites. It is clear that they were heavily used as a garment closure.  Japanning is a method of coating a surface with a mixture of oil and mineral pigment. Originally, lampblack was used to get a black finish. Successive coats of the varnish were heat-dried or polished to achieve the hard finish and deep luster imitating more expensive lacquerware. It was employed extensively in Europe from the mid 17th century onward, for items as large as tentage, and as small as the hooks and eyes featured here, a large size for heavy duty and military use. They are an inconspicuous means to cock a hat.

#124-1125, Black Japanned Hook & Eye, 1 1/8" long hooked
   $.75/ea.