H.P. (Henry Purdon) Sinclaire, Jr., (1864-1927) was involved in the glass industry in Corning, NY, for many years. He worked for T.G. Hawkes & Co., first as a bookkeeper, then quickly rising to partner and director at the company. In 1904, Sinclaire opened his own firm in Corning specializing in engraved glass in partnership with Marvin Olcott. The company's products were sold at department stores throughout North America. When the company had trouble finding enough high-quality blanks, Sinclaire partnered with three brothers - Ivan, Walter, and John Larson - to open a factory in Bath, NY. The blanks made there supplied both the Sinclaire firm as well as others. As the market changed, the company adapted by adding product lines such as undecorated colored glass and institutional items (including communion cups and votive candleholders) to its offerings. Sinclaire also developed a heat-resistant glass called "Radnt" that was made at a factory in Dunkirk, NY, and sold in hardware and department stores.
H.P. Sinclaire, Jr., passed away unexpectedly on June 21, 1927. With this sudden change, the company began shutting down. The Dunkirk factory closed first, followed by the Corning plant about a year later. In total, Sinclaire's company had operated for 23 years.