Dumb question: Easy magnet identification?

[Spence]

Old Gibson magnets are individually cast. I don't know of any other manufacturer who was using magnets of these dimensions at the time which suggests that being true, Gibson couldn't have been using someone else's rejects.

( Sorry Possum, I hope you don't feel like I've been picking on you lately. It's just a different point of view and line of logic, nothing personal).

The dimensions of a magnet as well as the grade of AlNiCo detrmine the amount of guass a magnet can hold. So if you know the original manufacturer you can look up their recipes for the various grades of AlNiCo they were making at the time.

By fully charging each magnet and allowing them to settle, you can then measure the gauss and make a much more reliable assertion as to the grade a magnet is.

You can also look at the magnets under a microscope for further clues to the composition.

[David Schwab]

Old Gibson magnets are individually cast. I don't know of any other manufacturer who was using magnets of these dimensions at the time which suggests that being true, Gibson couldn't have been using someone else's rejects.

More pieces of the puzzle, from the 1978 Seth Lover interview, by Seymour Duncan (SWD):

SWD: The “patent applied for” magnet was 2.5” long

Seth Lover: As I recall I think it was called a #55 magnet. 2.5” long X .5” wide X .125” thick. That was the nominal dimensions. The length could vary +/- 16th inch--wouldn’t matter too much. The width had to be held close to .5” if you wanted to keep your spacing right. And the thickness, that could vary +/- 1/32nd”. You could still put the coil assembly together.

SWD: Did the magnets come from Indiana General back then?

Seth Lover: Oh, I think they got some--G.E. had a magnet plant around Midland, Michigan--somewhere up in that area. I think they supplied them for awhile and down in Indiana--Indiana General. Then there’s another company that I can’t recall that we got some from. I think Gibson shopped around-when they got down low in magnets they shopped around with the different suppliers-- whoever could supply and make deliveries at the time that they needed them and had the best price were the one they got them from. Because Alnico at the time was getting pretty common-- everybody could make it and had the facilities.

That makes it sound like they had several vendors, and that was a standard size magnet... a "#55"

But I'd imagine back then Gibson said what size they wanted and then the magnets were made for them.

[Possum]

....

Jim at WCR told me he had a conversation with an old magnet company salesman from back in those days, who said that Gibson always bought their reject magnets and always wanted the best price. Did they do this with every supplier, I dunno. Gibson was cheap back then and they still are, nothing's changed. I think ALL alnico bars back then were individually cast. It looks like to me that maybe around '62 they started cutting them from blocks like they do now. I've had a couple companies get Chinese companies to do rough cast magnets last couple years and they've been individually cast as well, they have the exact same mold markings on each magnets, from several distinctive few molds. I have several P13's and the magnets in those things look horrible, literally burnt on the skins and one of my early patents has a similar magnet. Burnt so bad that they don't conduct electricity on the skin. So, I don't know, thats what I've been told and what I see from period magnets from P90s, P13's and PAF era. I don't know what a "reject" magnet would have been by those terms back then--wouldn't hold a typical charge--too thick--burnt too bad--wasn't fully in the magnetic field when cooling and thus non-oriented? Don't know :-) No problem Spence...

[Mike Sulzer]

I have some alnico 2 that will hold nearly a 700 gauss charge like alnico 5 will.

Is there a standard way to measure these magnets? That is, a method of making sure that the field sensor is in the same position with respect to the magnet each time a measurement is made? Otherwise, measurements made with different meters by different people are not comparable.

[Spence]

Is there a standard way to measure these magnets? That is, a method of making sure that the field sensor is in the same position with respect to the magnet each time a measurement is made? Otherwise, measurements made with different meters by different people are not comparable.

You really need to move the probe over the whole face of the magnet.

[Possum]

...

Guass meters are pretty standard, they use hall sensors and are digital. They are all pretty much the same with different housings. In the old days people used magnetometers, basically a spring meter that measures pull, Duncan still uses these and I think Fralin does too. They don't measure gauss, the highest reading on them is 25 or 50 :-)

[defaced]

Is there a simple method of verifying composition?

Nothing that you'd want to pay for. Where I get optical emission spectroscopy (OES or arc spark method) done for work costs 150 bucks a sample - and you get a 1/4" round burn mark on your sample. That's the cheapest way I know to get chem results.