First off, I've never been much of a slide shooter, so I admit my ignorance on this. In the assorted stuff my parents have sent me from my late grandmother's house are a few boxes of old slides (most in Kodachrome mounts). They range from my dad's childhood (1940s) to the early 70s. I have a project in mind using them that would mean projecting them (and maybe for a minute or two). How safe is that and how long can a slide be projected before there's a chance of damage from the heat of the bulb? I've really only projected slides for a few seconds each in an average show and very rarely.
And, as a side note, yup, the colors of the ones in Kodachrome mounts look perfect and the other ones are a little off.