As you had gleaned, Mikael, Diamant frames are Belgian..and must not be mis taken with DIAMOND which is also Belgian.
This reply is by way of a first snap-shot explanation and may be very sligh tly inaccurate, but by and large, correct. I will try to write a more accur ate one later after some thumbing through my scribblings of some years ago.
DIAMANT was the brand name on frames produced for and sold by one of Belgiu m's larger lightweight wholesalers. Belgium only had a very small populatio n - is it about 12 or 13 million , but had a large number of excellent ligh tweight suppliers. The largest probably was the liaison of M and Mrs Desnercke of VELTEC, o f Gavere, with Piet Rentmeester, of RENTMEESTER of Yerserke in Zeeland, Holland.. The third member of this trio, Jose Alvarez of Auch in France, having agreed to join the triumvirate, decided to pull out, declaring that his company was strong enough to take on the challenge posed by the Veltec- Rentmeister alliance, throughout Europe. This alliance frames produced u nder the name of CONCORDE.
DIAMANT belonged to the wholesaler, Simons, from Bekkevoort in east ern Belgium not far from Eddy Merckx's place. The frames varied from fairly straightforward amateur training frames built from FALK tubing , of which a lot were robust cyclo-cross ones, through to custom-build ones such as Mi keal's. I think that all were built in belgium, unlike the Concorde's th at were mainly Italian (some from CIOCC), although some were Belgian fro m- Van Yperzeele of Geraardsbergen . RIDER was a sub-marque of this compa ny
The cheaper frames were made by a largish specialist frame - nothing but fr ames - manufacturer called DIJA, owned by A .Oosterlink and his sons at Pit tem-EGEM, not too far from Ghent and Oodenarde.
However the quality frames were made by a one-man company, whose name I for get for the moment but whose workshop, a long narrow one, built out in th e backyard of his house, was just up the road a few hundred metres from DIJ A. His output was very limited by virtue of the fact that he did everyth ing himself..and I recall him suggesting that, apart from Eddy Merckx, he w as the only constructor of lighteight hand-built frames in Belgium..and wha t Eddy and the likes of CIOCC ( also to Paganini) did not supply to Belgium , he did. A lot of his frames, curiously for Belgium that is, were made from Ishiwata tubing, particularly the O17 and O19 series. However this is due to the fa ct that he built frames, probably the bulk of his production, for the godfa ther of the Belgium lighweight industry, a very elderly gentleman, Mr Wit berg, who ruled from his penthouse suite overlooking the North Sea at Ost end. he was, at the time the largest wholesale of Shimano products in Europ e, of Tange, Araya, SR, and also of Ishiwata. The frames were supplied into independent retailers. When Shimano decided to set up its own HQ and w arehouse in Europe it bought out Witburgs comany and one nearby over the bo rder in Holland. This one-man band company was so small that I passed it by about five times before a local garage pproprietor told me to knock on the front door of a certain house in the main street of tiny town. Until one had passed throu gh the house, then through the passge that was his workshop and exited via the garden, the only indication that it was a frame shop was a couple of du stbins in the tiny garden with damaged frame tubes projecting from their ri ms.
Diamant, a powerful company in competition with VELTEC-RENTMEESTER, also im ported Alan, Guerciotti and GIOS
DIAMOND on the other hand was a builder of a lerge range of standard bikes and frames, including some half decent lightwieghts...but factory produced. ..not by hand. This company is still in production in Liege.
The final main link in the Belgium lightweight chain was CODAGEX, who imp orted Colnago, Suntour, Sugino, Panaracer and also TVT..more often than not in the early 90s badged up as Pinarello.
Norris Lockley...Settle UK..thinking that I will probably never remember th e builder's name...but he built excellent frames well worth remembering