Instructions
Examine the hinges on the doors of the buffet. The butt hinge, which was used from 1815 to1840, was made with a lot more metal than the thinner hinges used after 1840.
Check the types of screws that are in the hinge. Older screws will have uneven threads and the slot in the top of the screw will be more narrow than a modern screw. The machine cut screws of the 19th century were not made with pointed ends.
Pull out a drawer on the buffet. Check the construction of the drawer to see how it was made. The dovetailing construction will have fewer joints the older it is. Earlier pieces of the 18th century were made with one large dovetail joint or it was constructed with pegs. Dovetails were cut by hand and will not be even and straight. Ninteenth century dovetailing improved in that these pieces were made with 4 or 5 dovetail joints.
Check for newer screw holes behind the drawer handles. If the hardware has been replaced you may see the older holes on the inside of the drawer.
Check the wood on the back of the buffet, older pieces will have odd sizes of boards because the builder probably cut his own trees and used whatever size lumber he had. The saw lines in older pieces will be straight and newer pieces will have circular saw marks.
Check for very small grooves in the wood surface. Older pieces were planed to smooth the surface and it may be uneven.