Jambiya question

[Sajen]

Dear members,
I have a simple question for the experts. I've handled a lot of edged weapons, but with very rare exceptions, I've always avoided Yemeni jambiyas, firstly because I'm not familiar with them, and secondly because I've noticed that some have hollow blades, meaning the blade consists of two pressed sheets of iron soldered together. I simply wanted to know if this is common, especially in older pieces. The blades usually have a pronounced central ridge; does this also occur in forged blades?
Some information on the subject is given here: http://www.vikingsword.com/vb/showth...hlight=jambiya

Regards,
Detlef