In article , fred writes

There may be more info at http://www.pilkington.com but they don't half
make it hard to find. If it bothers you I imagine they will do Optilam Phon in
low-e as well. Be sure to buy from/as trade if you can.

Ah, here we go:
http://www.pilkington.com/resources/...ndatasheet.pdf

Examples are 16mm gapped but I'm sure 6.8/12/6 would be just as easy
to have made up.
--
fred
Plusnet - I hope you like vanilla