Buttons have been made for the past 4000 years at a minimum - Indus Valley Civilization is credited for the first ones. In British Columbia, buttons (esp. mother-of-pearl, or shell because of their reflective qualities) were a valued trade item for decorating blankets, clothing, etc.

Buttons have been made of basically any material that would work: bone, most metals, wood, shell, horn, glass, ceramic, bakelite, celluloid, lucite, vegetable ivory (from palm tree nuts), etc. If you find a button at a BC site, if it is ceramic, glass, shell, horn, or bone, it could pre-1846 and should be collected. If it is bakelite or plastic or vulcanized rubber, it will date later. Prosser buttons - made of porcelain with a smooth top and an orange-peel bottom post-date 1840 but should be collected - but be careful, plastic buttons were often made to look like natural materials and you may confuse a shell button for plastic. Jet (shiny black coal, basically) became popular after 1851. Earlier buttons will be less refined than the older ones. In BC before 1846, we should expect to see numerous shell (also called 'Pearl') buttons as they were trade items, and very simple buttons made of cheap materials from sailor's uniforms, clothes, or trade.