The mercury acts as a catalyst, so it isn't consumed per se, so that afterwards, all of it can be removed from the felt. I am sure if you were to take a victorian era piece of felt you would find some mercury in it. But in terms of the victorians, their wallpaper was much more dangerous. It was a bright green color loved by the middle class. The problem was it was made with Chromium VI, which when exposed to moisture, would end up in the victorians.