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Such pieces without obvious maker's marks are often to be found, on the face of it, it seems very strange that someone should make a reasonable quality product, mark it as sterling, but then apparantly deliberately avoid placing their name to the product.
Over the years I've developed a personal theory on the origin of such pieces, but it's only my own thoughts with litte to back it up. I think such pieces are what is known in various trades as 'Premiums'. The idea of 'Premiums' is that a manufacturer will make a special offer to boost sales of certain products, the special offer would be a give-away or an offer of something at a very attractive price. Kelloggs, for example, sold cutlery from the back of their cornflake packets for years, Maxwell House gave away coffee spoons, Colmans offered mustard pots, etc. etc. Such give-aways or special priced offers were 'self-liquidators', Kelloggs would make no profit from the cutlery sales, but would be rewarded with repeat sales as customers built up sets of cutlery and flatware at the special prices and thus maintaining customer loyalty.
To make such offers appealing to the customer, flatware had to be sourced at incredibly low prices, in the past, major silverware manufacturers would have turned up their noses at working for next to nothing, but during the 1950's/1960's period cheaper imports from far eastern manufacturers was really starting to bite and the opportunity to keep their factories in production, if only at break-even levels, could not be ignored and the 'Premium' business was welcomed by the manufacturers, but not openly as the last thing they wanted was to devalue the 'bread and butter' lines of their business, thus they produced flatware by the thousands, usually unmarked, they maintained anonymity as the maker whilst keeping their own profile high with their regular marked lines.
It would be great if any members who were working, or had knowledge, of the silver trade at this time could confirm/deny the above as the source of such unmarked pieces.