[Peter Ward]

I've been doing a but of research on mirror coatings lately, spawned in part by the claim below:

"ALL OUR (made in China) RC TRUSS TUBE ASTROGRAPHS INCLUDE...

............Hyperbolic quartz primary and secondary mirrors with 99% reflectivity dielectric coatings in all GSO RC truss tube models!"

I've concluded this is pure crap.

While it is possible to dielectricaly coat primaries, if you have a NASA sized budget...this process distorts the underlying optics and is normally only used on smaller optics where only the central section being used (eg diagonals or flats).

So what do we make of the claim above???

Sure sounds cool.

I strongly suspect these mirrors are simply aluminium coated, with a quartz overcoat.

To be fair, a quartz overcoat does have good dielectric properties....but this is not the same as a dielectric mirror coating!!
(it's a plain mirror with a dielectric over-coat at best)

A small dab of ferric chloride on the mirror will prove my thesis beyond reasonable doubt. It will eat aluminium...but won't hurt a dielectric mirror.

I also suspect not many punters will be soaking their RC mirrors in ferric chloride to see whether I am correct.

P.S.
Consumer law in Australia would likely allow you a full refund if the product was not as claimed.