A picture sent to me by Michael Talbert. He believes the packet dates to around 1940.

Gaslight printing paper was a slow (i.e. relatively light insensitive) paper used for making contact prints. "Contact" prints mean prints made by clamping the negative into close contact with the printing paper, hence the resulting print is exactly the same size as the negative. Such a printing method was frequently used when negatives were large enough (plates or large roll film sizes) to produce worthwhile 'same-size' prints. But the advent of miniature 35mm film cameras mostly made such a printing method obsolete.

The name Gas Light refers to yellow coloured light, as produced by 'Towns' gas when burnt in gas mantles for home lighting. The paper was largely insensitive to such light and so contact printing could be carried out in what was, until the 1920s or even 1930s, normal room gas lighting. But the term (and the paper type) persisted into the electric light era (as with this 1940 packet), though it was necessary to take more care to shield the paper from direct light when using it in a room lit by electricity. By the 1950s, this type of slow, silver chloride based, printing paper was (correctly) renamed as Contact Printing Paper.

The pack of paper shown here is of ¼plate size (3¼" x 4¼") of Normal contrast grade, single weight (i.e. thick paper rather than card) and with a glossy surface (though requiring glazing to bring out the full glossy potential. Glazing involved squeegeeing the wet print (from its final wash) onto a sheet of glass and allowing the print to dry. With luck (!) the print would fall off the glass when dry and would have a perfect mirror glossy finish. Commercial printing laboratories used heated chromium glazing sheets rather than glass.

Michael points out a mystery with the labelling of this packet: "The code on the Selo packet is definitely S31P, which is odd as the paper is labelled as Normal grade, while 3 usually refers to a Hard or Vigorous grade.
My 1940 Ilford book gives three grades for Selo Gaslight contact paper but doesn't give any numbers for the grades. In the same book it lists all the Ilford Bromide papers, grades 1 to 6, and within this numbering system Grade 3 is Vigorous grade and Normal is 2. So why is this packet of Normal Grade given the grade 'tag' of 3 ? I can’t explain this one; its a mystery !