Whenever I do some silver soldering, I use my stock solder which is a bundle (about an inch diameter) of 1/16 wires which I must have ‘aquired’ some time ago!
Its all I have ever used – but I dont know what it is!
Not easy without any markings on the rods . The only thing to do without metallurgical analysis is to test the melting point against samples of silver solder of known specification . I wouldn’t actually worry about it too much – for any purpose except boiler making if the stuff melts easily and flows nicely it is probably ok .
Must have rods of known specification for boiler making though .