A 2008 update with the release of the Smoking Kills quest allowed players to craft a black mask and other slayer items into a Slayer helmet, provided they had acquired the ability to make the helmets. Slayer helmets are valued because of their effects and the fact that they are not tradeable. This update, together with a rumour of lowered drop rates by monsters, was responsible for a steady price increase of the black mask, from approximately 400-500k coins to well over 900k, due to increased demand for the mask to make Slayer helmets. Two weeks after the update, however, prices for the mask began dropping in the Grand Exchange, and soon thereafter mask prices were back to the 400-500k range. More recently, the black mask has made a steady rise and stayed briefly at around 940k, and is now currently hovering at around 1.6m, and rising. Recently it has been increasing in price due to the update which added the Hexcrest and Focus Sight used in the making of the Full slayer helmet which also requires a Black mask to make.
