By 1850, and perhaps earlier, Clarkson was making sash mortising machines. He and his sons subsequently received patents related to sash pulleys and mortisers. Mortiser and other woodworking machinery patents were granted to various members of the Clarkson family in 1877 through 1907. By 1896 a son, Frank S. Clarkson, and a grandson, Frank S. Clarkson, Jr., were officers of the Norris Sash Pulley Co. In 1906, Frank S. Clarkson was granted a sash-pulley patent that was assigned to the Clarkson Manufacturing Co.

Ad for Joseph Clarkson & Son, from 1860 "Baltimore Directory"

Information Sources

• We learned of this maker via an owwm forum posting by Matt Hankins.
• The 1850 Annual Report of the Board of Managers, of the Maryland Institute for the Promotion of the Mechanic Arts, lists Joseph Clarkson of Baltimore as "made and deposited" a mortising machine at that year's Third Annual Exhibition of the Maryland Institute. Available through Google Books.
• Woods' Baltimore City Directory of 1860 has an ad from this maker: "Joseph Clarkson & Son, Engineers and Machinists, No. 75 N. Front Street, Baltimore, Md. / Manufacture to order Steam Engines and Boilers, Vertical and Circular Saw Mills, Chair Back, Fellow, Scroll and Cross Cut Saws, Mill Gearing, Shafting and Pulleys. Woodworth's Planing Mills for Floor, &c., Sash Machinery, full sets. Also a general assortment of Machinery for Sawing, Planing, Turning, and Carving Wood in any desired shape."
• Listed in the 1874 work, Wiley's American iron trade manual of the leading iron industries of the United States, under "Steam Engine and Machine Works and Iron Foundries of Maryland...Baltimore": "Joseph Clarkson & Son.—Machinery."
• A notice in the Acts of the Legislature of West Virginia lists The Norris Sash Pulley Company, "manufacturing and selling sash pulleys and other classes of hardware", as having a corporate charter issued May 1, 1896. The corporate officers included Frank B. Sloan, Frank S. Clarkson, and Frank S. Clarkson, Jr. Sloan was co-inventor or co-assignee of several Clarkson patents.