If this is Thursday it must be postcards, 236

Hudson Bay Blockhouse, Sault Ste. Marie, Ontario, Canada, ca 1939
 

This 1939 postcard shows the Hudson Bay Blockhouse, Sault Ste. Marie, Ontario, Canada and was issued by Photogelatine Engraving Co., Ltd. Of Ottawa.   Photogelatine also called Collotype was a process invented in 1856 by the French chemist, civil engineer and photographer, Alphonse Louis Poitevin, and was used for large volume mechanical printing prior to offset lithography.  The process allowed for very fine detail to be printed the equivalent today might be compared to 1000 dpi. 

Without going into too much detail the process involved a plate of glass or metal coated with gelatin or other colloid, left to harden, then coated with a thick layer of dichromated gelatin and dried carefully, washed in controlled temperature water, then exposed with the negative using an ultraviolet source.  To make prints the plate was dampened with a glycerin and water mixture then blotted before inking with a leather or velvet roller.  The resulting prints required less pressure than stone lithography and could be made by hand but a press was more effective.  Business cards and invitations were also produced using this method since it allowed for fine detail of script lettering.

The Clergue Blockhouse in the picture was originally a powder magazine built of uncut fieldstone around 1819 by the British North West Company.  The simple design was typical of The Hudson’s Bay Company incorporated the stone magazine into their trading post in Sault Ste Marie, Ontario.  The stone walls are the only remains of the North West Company Post in Sault Ste. Marie.  Added in 1894 by Francis H. Clergue, an American entrepreneur, the upper portion of the building is made of logs and designed to look like those constructed during the Indian Wars one hundred years earlier.  Clergue used it as his residence and office.  The Blockhouse was used as a residence for several years but eventually fell into disuse and was burned in 1974.  In 1996 it was moved to its current site and restored as a historic site.

For more information, see:

http://fortwiki.com/Clergue_Blockhouse
http://www.historicplaces.ca/en/rep-reg/place-lieu.aspx?id=5595
https://en.wikipedia.org/wiki/Collotype