Photographers created their own supply of negatives in the 1850s by coating a piece of glass with a new substance, known as collodion. The light-sensitive silver halides in the collodion captured and preserved the image during the photographic process.
If you have glass negatives in your collection, they are probably sitting in a box that is too heavy to lift. Photographers used to store these plates in wooden storage boxes with dividers to protect the glass from breakage. Glass plate negatives, being both heavy and fragile, also require special storage care.
Steps to take when moving or re-boxong glass plates can be found in Preserving your Family Photographs.