About variable capacitors, which are essential for tuned circuits

In a tuned circuit consisting of a coil and a variable capacitor, even if the Q value of the coil is high, unless the Q value of the variable capacitor is also appropriate, performance cannot be achieved.

Comparison of air variable capacitors and poly variable capacitor
Air variable capacitor only have air between the metal pieces and an insulator that supports the metal pieces.
Therefore, an ideal Q value can be obtained.
Poly variable capacitor are made smaller by sandwiching an insulating sheet between metal pieces.

Some people say that the performance of poly variable capacitor is not very good compared to air variable capacitor.
So what actually happened?

So I thought I'd compare them, but unfortunately I don't have anything with the same capacity.
For example, if the manufacturer's variable capacitor is 430PF, the Q value is measured at 100PF or 200PF.
I compared the Q value of air variable capacitors and poly variable capacitors at 1MHz.
I used a variable capacitor that I had as a sample, but used variable capacitors or variable capacitors that have been used for a long time tend to have a lower Q value.
This is especially the case if there is dust stuck between the blades of the air variable condenser.
Do you mistakenly believe that even if the air variable capacitor has dust stuck between its blades, it will perform better than a poly variable capacitor?
Poly variable capacitors have an advantage over air variable capacitors when it comes to dust when it comes to sealed objects.

Comparison of Q value at 1MHz using Agilent (Keysight) E4980A LCR METER.

Left side: Used 430PF / 3-unit variable capacitor, New 430PF / 2-unit variable capacitor,
Used 2-channel AM / FM variable capacitor, New poly variable capacitor

Measurement frequency: Measured under the same conditions of 1MHz / 1V.

　
This data is for a new 430PF/double variable capacitor (Alps C624A).
The performance is outstanding!

　
This data is polyvaricon.

　　
This data is for a used 430PF/triple variable capacitor.
A decrease in Q value was observed. 　
You can see dust between the blades, so this may be one of the causes. 　
Since there are no new copies of the same item,
I can't draw a definitive conclusion, but I'm sure you can't go wrong.

　
I tried removing dust with a soft, thin brush between the blades of a used triple variable capacitor.
I don't know if the dust near the middle of the blade still remains, but the Q value has increased considerably.

Use a thin, soft makeup brush

Since dirt is the enemy of air variable capacitors, we recommend cleaning them frequently.