OT, Historical Photo Question

Sorry to clutter the list with this but I don't know of a more
knowledgeable group to ask. A friend sent the following inquiry so any
info is much appreciated and will be forwarded to him with the
appropriate credit line:

> Some "old time" black and white photographers use to take two
> photographs, one for foreground and one for sky and "meld" them some
> how into one plate (back in the days of glass plates). Just at a talk
> with Robert Glenn Ketchum who was talking about it. Do you know what
> photographers there were, the name of the process and where I might
> find out more info on it?

Thanks for helping!

Dan

-- 
www.danburkholder.com
www.tinytutorials.com