Martin, thanks for the response, that's precisely the line I was referring to.

I wondered if that could be the case; I know that even the most careful of researchers can be mistaken. Perhaps it is corrected in subsequent editions? My book is from 1946 (IIRC), 1st edition.

However, Struan's post puts us back in contradiction; saying that the reflector will strengthen the effect.

Can the reflector remain for viewing or not? that is the question

It seems that with the reflector present, there would be no way to produce a black.