these black dots on magnets annoy my mind

[Lollar Jason]

"But how to consider modern expensive pickups?"
Some people have lower quality concerns than others, I know a number of people that wouldnt use magnets with voids like that.

[vitaliikit]

"But how to consider modern expensive pickups?"
Some people have lower quality concerns than others, I know a number of people that wouldnt use magnets with voids like that.

if it’s really bubbles .. then I also would not want to deal with such magnets.
I have never come across such bubbles, so I went in cycles in these pictures.
Such magnets are slightly defective and not aesthetic for new pickups .. but tough guys make expensive pickups and install such magnets with bubbls in them.
HM .. Where is the meaning?

[Lollar Jason]

Its really bubbles- I have overseen and made hundreds of thousands of pickups- other people here are not slouches either and have made thousands of pickups or more and for sure seymour has stopped by- hes way beyond me as far as practical experience- rick turner lots of guys then there are members that are more into engineering so a wide range of experience . Welcome to the wild west- there are no pickup police there are no industry standards- more than half of the people making pickups couldnt even be counted as having production or engineering experience and there is alot of Bull shit being told to customers but on the other hand there are plenty of real people kicking ass and taking names. Dont believe it if you hear fantastic claims and just because someone claims to be the best- check it out. in fact if they claim that its extremely suspect IMO. There are a number of companies that sell a story- in the USA there is a phrase "sell the sizzle not the steak" I am sure there is a phrase in every language that means the same thing. Companies have come and gone for the last 25 years- more go than stay probably 95 percent have gone- the wonder of the internet it equalized the playing field which was good in ways but bad in others- any yahoo can proclaim their superiority LOL Sorry your world view has just been bent- you can buy pickups with no cosmetic problems if you look around

[Mick Bailey]

Gas bubbles that are large enough will escape - its always the smaller bubbles that get trapped as the metal cools. They will always be towards the top of the casting because the gas rises through the liquid metal. As the metal cools, a skin forms around the bubble and furthermore reduces the buoyancy. In addition a skin forms on the top of the casting. So now the trapped bubble has the surface tension of two skins to overcome, which it can't do. So the bubbles lie at a predictable depth below the surface based on pour temperature, cooling rate and dimensions of the casting. There are techniques to overcome this, but these add to production costs.

Under microscopic examination you may find that even perfect looking magnets have some porosity. The manufacturer should have a documented quality control process with acceptance criteria for what goes out of the door. Maybe these would be classed as 'B' grade, but the final test is whether the pickup sounds good. You can bet if a pickup had these bubbles and was wound by Abigail out of one of SRV's strats it would suddenly be a must-have mojo feature and a bubbly pickup would somehow be better.

[Leo_Gnardo]

You can bet if a pickup had these bubbles and was wound by Abigail out of one of SRV's strats it would suddenly be a must-have mojo feature and a bubbly pickup would somehow be better.

Thanks Mick, that makes my day! How many thousands of hit records have guitar tracks on them recorded through pickups that not only had magnet "defects" but (horrors!) were never examined!

Once again, the "sound" is in the player's hands, or brain-hand connection to take it one step farther. Black tick marks or bubbles in the pickup magnets have nothing to do with it!

vitaliikit, you could make two lines of pickups. One with "perfect" magnets, their steel cast under hi vacuum conditions to eliminate bubbles, thoroughly examined & x-ray tested. The other with "foamy" mags, to approximate the ones actually used to make those terrific recordings ever since the dawn of the electric guitar. Charge super-premium prices, and declare yours to be the best in the universe - that's all it takes to be a big $ucce$$.

[Helmholtz]

As many original vintage Fender PU magnets had these bottom pits near the center, I would expect to find them in faithful ("authentic") reproductions as well. So rather a feature than a flaw.

[Helmholtz]

@ Mick Bailey:

You seem to know a lot about metallurgy and manufacturing processes. Do you know how cast AlNiCo rods are ground to shape? Some kind of lathe with an arbor involved?

[Chuck H]

I always figured they were cast as one long rod, then ground/polished to their diameter and then cut to length. So any inclusions would be random throughout. But if they are cast as shorter rods and gas bubbles tend toward one end or the other that would explain a tendency for them to be revealed when the shorter rod ends are ground to length spec?

[Helmholtz]

I have no doubt that cast AlNiCo contains voids to differing degrees. And the explanations given by Mick Bailey make a lot of sense.
But it can't be pure coincidence that all the pits I saw were at or near the center of the endface.
So even if they are sometimes found completely off-center, I assume some processing that favors their exposure at the center.

[Bloomfield]

Centreless grinder I would imagine, although I've never seen one that small myself.

https://en.wikipedia.org/wiki/Centerless_grinding

[Mick Bailey]

Yes, centreless grinding. Rods can be vacuum cast as a long rod, ground and cut into lengths. Individual slugs can be conventionally cast and again, centreless ground. You can go down to as little as 0.5mm diameter for this process. Bubble inclusions regularly appearing at one end of the slug indicates they're individually cast. I think the void-free magnets are probably vacuum cast.

[Helmholtz]

Bubble inclusions regularly appearing at one end of the slug indicates they're individually cast.

So we have some clue why pits appear in high percentage at one end. But I still wonder why they typically show near the center of the face.

[Chuck H]

So we have some clue why pits appear in high percentage at one end. But I still wonder why they typically show near the center of the face.

Well... The gas bubbles want to escape, but the outside of the case is cooling. I assume this increases it's viscosity toward the outer casting. That might explain the tendency toward center.?.

[Mick Bailey]

See post #9

[salvarsan]

Between two world wars, the German manufacturer Vacuumschmelze addressed the problem of cast voids by smelting under reduced pressure, a more costly procedure but justified by its low defect rate.

Since then, a mixture of demand, material science advances, and technical improvements led to the general absence of voids in Alnico magnets in particular and most metal casts in general.

Since the techniques for casting defect remediation have been known for a couple generations, their presence in modern products means a low-quality manufacturer.

Searching on "casting defect remedies" gets you some useful information.

-hizself