hard to find and always desirable original and remarkably intact c. 1860's american civil war-era single oversized "mercury" glass interior residential doorknob likely designed and fabricated by the nashua lock company, nashua, nh. the bulbous doorknob retains the original silver nitrate coating applied to the interior of the glass doorknob. the tapered shank is comprised of brass with a nickel-plated finish. great overall condition.