Digital BW, The Print

What is the recognzed 'archival' method of adhering a print either to 
a backing board or behind the window mat - is there a 
safe 'removeable' tape that wont damage the print/paper, or a glue, 
or must I use picture corners. In the old days, we used to tack the 
print with a hot iron and a 'seal' waxy/tissue product - I forget the 
name.