It is a long established company. In 1919 this was the company that brought out the the totally new concept of self-filling pens. They were the first of their kind. Then in 1925 they were the first to introduce replacement nibs for pens. During the Second World War, Platignum was commissions to create spy pens. These were pens that could conceal compasses and maps.
This company is not to be confused with the Japenses pen company - Platinum Pen.
It all started with the Mentmore Manufacturing Company in London (1919). They introduced self-filling fountain pens with gold-plated nibs. A totally new step for pens at the time. They introduced the Platignum brand around 1925 as part of a reorganization of the company. Platignum, as a name could not be registed as it is the name of a metal, so they introduced the Platignum Pen Company. The Platignum branded pens was mainly in the low-end production type, when compared to other pens.
In 1925 with the introduction of interchangeable nib and injection molding for plastics parts, the company took off.
By the 1930s to the 1950s rather than be a segment of Mentmore, Platignum became the dominant part of the company.