Vintage DD turntables. Are we living dangerously?

Dover,
I don't doubt your results. They are what they are. It's the explanation that doesn't add up. The Goldmund platter is designed to match the mechanical impedance of the record with the surface adjacent to it. A steel or copper surface directly underneath the record is a different approach.

I don't blame science or lack of, for the vagaries of platters/mats. A mat is designed to work with an existing platter. As your results indicate (VTT1 & Verdier) there are too many variables to call this science.
I assume the Counterparts mat is the one Sota called Supermat (80's). It's different from Goldmund mat. The plastic formula is softer and I believe the Goldmund mat has no layer of lead.
As the names indicate acrylic and methacrylate are closely related. Delrin is DuPont's trade name for acetal homopolymer and like copolymers, can be formulated for differing hardness. Most platters/mats are probably made from copolymers and their exact formulation was/is a trade secret. The Goldmund mat seemed slightly harder than their platters, but this perception could possibly be influenced by thickness.

What then is the goal with an aluminum platter, to dampen the platter or match the record impedance? Perhaps both?

Regards,

What are the measurable physical properties of lead that could support the contention that it is superior for a platter or whatever other use in audio, including making capacitors? Furthermore, what is one looking for in such properties? This consideration will only engender another bunch of subjective opinions; I am not saying lead is right or wrong. Nor am I saying that I prefer any other material to lead. But our arguments are circular, always leading back to the fact that we are trying to connect our subjective opinions to physical facts, and the physical facts can be used to support one's argument in almost any way one wants to use them. What is missing is an objective way of assessing platter performance that is truly meaningful, and then the capacity to vary the properties of the platter to see how they affect that objective parameter of excellence. Ain't gonna happen. Call me a nihilist.

Gentlepeople.
I'm with Lewm.
"What is missing is an objective way of assessing platter performance that is truly meaningful"

There are so many different approaches out there and a bunch of them perform brilliantly, yet often they contradict each other in design philosophy. One would think that designers would gravitate towards a common theme if there was one path towards the holy grail..... It seems not.

On the topic of adding weight above the manufacturers original design. The thought here that increasing (or decreasing) the moment of inertia, "I",too much would upset
the time constants and gain profile in the feedback loop. I agree that it should be considered. I took great care when discarding the original SP10 MK3 platter and replacing it with my own design, to keep "I" close to the original.

The LO7D is a special case since the outer ring clamp greatly increases the platters moment due to the concentration of its mass towards the circumference. It therefore makes sense to offer a switchable setting for this.

On the other hand Artisan Fidelity offer a, presumably heavy, copper matt for their SP10's. Albert Porter uses a Stainless Steel matt on his simply stunning MK3 rig. A customer of mine, Pass Labs, makes a stainless steel platter to replace the original SP10 MK2. From photos I have seen it is likely that "I" has been increased.

With the SP10 range, at least, there seems to be a high tolerance for different platter moments.

Lead seems like such a good material for audio, right? Not too hard, not too soft. Yet lead is one of the worst ideas ever foisted upon well meaning, naive audiophiles. Even in small amounts it screws up the bass response and lower midrange. Gag me with a spoon.

Regarding the inertia of the platter & servo mechanism, Yamaha GT2000's original platter is ~5.5kg, but Yamaha offered as options a vacuum platter mat (~2.2kg) and a gunmetal platter (~18kg). So if you used the vacuum mat with the gunmetal platter, you'd be at roughly four times the original platter's weight. The shape of the gunmetal platter is the same as the original aluminum platter's shape, so presumably the inertia to weight ratio would be about the same too.

So at least in this case, the manufacturer did not consider a very wide range of weights to be a problem.