The Mentmore was founded as Mentmore Manufacturing Company in 1919 in London, and owes its name to the location of its first office in Mentmore Terrace, Hackney, London. Initial production was o automatic filling models (?) and gold-plated nib.
Roughly in 1925 was introduced the Platignum brand; at this time it seems there has been a kind of reorganization of the company. It seems that the intention was to use the name Platinum, but that this was not registrable as a trademark since it is the name of a metal, so the name was changed slightly and the Platignum Pen Company was created, that began marketing Platignum branded pens, focusing on the low-end production in comparison to the pens distributed with the main brand.
Still about 1925 it is claimed the creation of an interchangeable nib group, and the production of pens with injection molding plastic parts, two facts that will place the company ahead in both inventions. While the first claim is supported by a 1924 patent (nº GB-237472) there is no clear evidence about the second claim, but in a 1949 advertisement for a subsidiary dedicated to production of injection molding plastic parts, there is a claim of more than 20 years experience in the field.
For some time the two brands were produced together; the Mentmore was transformed into a joint stock company in 1930. The situation at that time is not clear, there are those who reported that the brand Mentmore has been progressively replaced by Platignum, but by the late '30s to the' 50s, there is a large production of pens with this brand with explicit reference in advertisements to the "Mentmore Manufacturing Company". Also a patent of 1936 (nº GB-457212) explicitly shows the name of "Spot Pen Company" as the new name of 'Mentmore Manufacturing Company". However the "Spot Pen" name appears in an advertisement for the British Industries Fair of 1929, while maintaining the reference to the company as "Mentmore Manufacturing Company". Association with Platignum brand is established at least until 1957.
Around 1939-1941 (?) was produced the Mentmore Paramount model, an imitation of the Waterman's Hundred Year, it was also a plastic resin lever filler pen, and with a decorative transparent plastic bottom similar to that used by Waterman. The pen, however, had more slender lines. Another imitation is the Mentmore 46, an hooded nib button filler pen, which was clearly inspired by the Parker 51.
There is, however, known production of pens under the Platignum brand name bearing "Mentmore Manufacturing Company" as a reference to the manufacturer through the 1950s and presumably beyond, and it is unclear the terms under which either brand name was used, the company appearing to have adopted the Platignum name in 1981 (as reported by Grace Guide, which cites the May 1, 1981 issue of The Times). Today, both Mentmore and Platignum exist as independent trademarks.
Translated with www.DeepL.com/Translator (free version)
-  company history, from its old website.
-  company data on Grace Guide website.
-  short history with some model name and photos.
-  discussion with some historical informations.
- this date, like the others for which no precise reference has been indicated, comes from the page dedicated to the company on the Grace Guide website reported in the references.
- thanks to these instructions in which reference is made to the Stevenage site to which the company moved, according to what's reported by Grace Guide, in this very year.