had they done any other 28" mirror blanks before yours?

what did the opticians who have worked these blanks have to say about the anneal?

what is the stated largest inclusion allowed before the blank is rejected?

cellular mirror blanks can even be less expensive than conventional blanks, because they use less material:

http://www.embeddedrf.com/Lookinglass_Webpage_Files/Webbed_Backed/Webbed_Blank.html