Got it .... From the B&W catalog: "Filters Special Effects Acessories From the Pros to the Pros":
The filter is a B&W090 "Light Red" - equivalent to a Wratten 25 or Hoya R25.
The filter factor is given as 5 - requiring a filter correction of 2 1/4 stops- close enough to the 2 1/2 used.
All I can say is "That is what happens when a B&W090 is used to photograph roses".
Thanks for the edification. I have no knowledge of B+W filters. Rereading the original post I don't see any referal to the brand of filter. I have often wished to see a comparitive chart of the various filters. There have been some implied work (A. Adams - Schaffer Vol I e.g.) but where is a comprehensive list?
Truly, dr bob.