Purple glass and old chair parts

     When glass is quite old and has lain for long periods, it takes on a purple color. Especially in the deserts of the west, collecters take great pride in finding purpled glass artifacts. This isn't the old west, by any means, but on several occasions, my wife and I have found purpled glass fragments lying on the sidewalk to leads from our driveway to the western rear entrance to the house. Strangely, pieces or parts of old wooden chairs are also amoung the glass. I far as I know, we do not have, other than these fragments, any naturally purpled glass in or around the house. The find is always first thing in the morning as we are preparing to leave the house for the first time that day. The fragments are thick and odd shaped like they came from some larger artifact that was three dimensional; not like flat windowglass. The wooden chair parts appear to be from chairs that were spendled. The wood is usually painted black, sometimes several coats of paint in various colors are evident.