Strange audible error on 1959 stereo disc

[Schetteb]

Dear plating and pressung specialists,
did anyone come across such an plating/pressing error? I found it on an old stereo lp from 1959 and i made a microscopic Investigation, since that error is very obvious in the sound. Has anyone an Idea what caused that deformation of the groove bottom?
Kind regards
Bernd

[andybee]

maybe the stylus has scratched the aluminium surface? or there was another thing under the laquer,
some sort of primer or another layer of laquer... how does it sound?

[Schetteb]

The grooves are not as deep that I would think about a cut into the aluminium disc. Actually i would guess that the master was cut with an advance Ball and without variable depth. The sound is a sort of crackling in the loud passages.

[Dub Bull]

Perhaps it shows that they 'polished' the stamper and thereby broke off the peaks of the mountains, forming high altitude mesas (on the stamper) and flat land zones at the bottom of the groove of your pressing... The wider groove sections, having wide, flat lands, instead of narrow valleys, would make a pickup stylus 'bottom out' - no longer being supported by the walls which are gone, there, whence the surface noise.

- Fr. José †

[Schetteb]

But why would someone want to polish the stamper? That makes no kind of sense from my perspective. I only know mothers beeing polished (dehorning).
Bernd

[farmersplow]

I have no (at all) experience and knowledge about Stamper! Therefore, there is a risk that my suggestion will lead to laughter.
My experience with stamping and pressing tools (which is at least a little) has shown me that the sharp edges of the stamping tool quickly wear out (get rounded) if the workpiece is too hard or the tool has been used too often.
So could it be that the stamper was used too often or the vinyl pucks in a batch were not soft enough and thus damaged the stamper?

[tamachura]

But why would someone want to polish the stamper? That makes no kind of sense from my perspective. I only know mothers beeing polished (dehorning).
Bernd

There is a certain chrome polished often used to polish stampers that have label moisture stains or very light scratches. From my knowledge and industry wide practice in an attempt to make the stamper viable before going to a new (and often non existent) one. If over polished the process can lead to volume drops in the that was worked on.

[Dub Bull]

Mothers are not said to be 'polished'. They're said to be 'buffed'. This is done because polishing the stamper face obviously hurts the sound. Buffing the mother is less harmful since the buffing is done mostly to the unused land. Both were done in order to facilitate the pressing operation and to make the pressed sides look good to the naked eye.

[Schetteb]

But somehow I cannot imagine that polishing a stamper or any other mecanical abuse of the stamper would cause these strange artefacts to the groove bottom.

Bernd

[Dub Bull]

Is there another scenario? The groove's center line reflection appears to be flattened only at the deepest (i.e., widest) sections of the groove, and the center line is still narrow and clean after the brief 'widenings'. Therefore, we know the cutting stylus tip didn't break, which would have ruined (as in, deleted or corrupted) the rest of the center line, if not the entire groove. Since there's no way an intact stylus tip can do this, it means the defect occured subsequent to cutting. That's why it's likely that something knocked the highest tops off the peak ridge of the (inverted, and, therefore,) elevated groove of the stamper. Since this was pressed in 1959, it was at a time when stamper-polishing was more commonplace than today. It's possible that they did more than just polishing. They might have been trying to de-burr the elevated groove turns. Something made the several highest peaks flat - after the cut - while leaving most of the groove-ridge intact.

[boogievan]

Is there another scenario?

The stamper ridge's ultra-brief nickel-peak (where the cutting stylus was moving within one half-cycle of vertical motion) could have gotten smashed flat in the press upon initial closing or over time and still seemed to make good pressings since the majority of the ridge was not crushed. But, yeah, they did polish stampers. I'd expect random angles more like chamfering than a 'low mesa' that's orthogonal to the groove, but it's so small a section it might well be mildly chamfered, innit?

[Aussie0zborn]

There's no reason to polish stampers. Polishing mothers removes the horns at the edges of the groove. This allows the stamper to separate easily from the mother and consequently, allows the pressing to separate easily from the stamper. Polisihing the stamper would wipe out fine detail in the groove walls.

[boogievan]

They actually did do a lot of stamper polishing, back in the day. Also, a major Midwest-American pressing plant was polishing stampers when they started out about ten years back. They switched to buffing mothers (with Mother's Rouge!) when their electroformer scolded them about wiping the elevated groove of the actual stamper. Private-message for deets - you won't believe what they wiped with... It's something that a presser thinks will help - and which does make the pressings look smooth, but a cutterist or audiophile would cringe at the thought...

[Aussie0zborn]

I would call that bad practise. In all my technical documents about electroforming from Europa, Ortofon (yes, Ortofon made plating equipment), Toolex, Capitol Records, PolyGram, EMI, Apollo and others, there is no suggestion that stampers should be polished. I can’t see how it stands to reason

[boogievan]

Right, innit? It was not any electroformer who ever polished a stamper. As I've been saying, it was pressing plants that did it, before installing them in the press. I Fibo-U-nacci. It also explains what happened to that center line - pressed by the broken-peaks of an elevated groove, if Fr. José is right, and he usually is, B'ruch haShem.

[Schetteb]

Could it bei something completely different than polishing? Maybe air bubbles during electroplating?
Kind regards

[boogievan]

Air bubbles in the think-tank? (; It would be after the cut, so, possible, since we at least agree that the center line of the cutting stylus was not ruined, despite the bulges where it made the deepest cuts, but it's extremely less likely that gentle bubbles broke the highest Nickel tips off the elevated groove (ridge) of the master than something more brutal such as stamper-polishing, which I aver was done by pressing plants occasionally, even though they should not have...

Fwiw, nickel record-growing actually is not the process known as electroplating, even though most people call it 'plating'.
It's accurately called, 'electroforming', since a completely new part is formed, rather than a finishing phase being deliberately permanently added (electrically) on top of an existing piece of metal. {When a non-conductive mandrel, such as a lacquer, is used, it must first be sprayed with a metallic coating, such as Silver Nitrate, in order to make a conductive replica of the groove. This causes the silver layer on the mandrel to reverse-plate onto the face of the new part, made of Nickel. It's not a desired condition, however, and the silver phase is removed from the master Nickel record before it's converted into a stamper. Nothing 'plates' onto the lacquer, and, when electroforming Nickel records from amorphous copper-plated disks, no Silver spraying is necessary, so, nothing even reverse-plates onto the copper, as its surface, like that of a father or mother, will be passivated, thereby precluding 'plating'.}


Both, electroplating, and electroforming, were invented by the Italian, Luigi Brugnatelli. There was a Luigi Galvani, but he was a surgeon who tried to study what he thought of as bio-electricity and then realized it was simply the same type of charge flow as all electricity. We get the word, galvanize, from his last name. But it was the other Luigi who brought is 'plating', and both Luigis initially were using, the third Italian, Alessandro Volta's pile battery. Viva Italia.