Well, If you want to get into technical reasons for the dirtier glass, here we go.23 pages of Blaze King talk on another thread and only one pic posted here in response to the original poster's request? And that one response praises the clear glass benefits of a Blaze King? I never considered a BK because of their reputation for nasty glass which was a negative to the #1 item on my list of "musts." What is going on here?
The king seems to have the dirtiest glass, due to the depth of the firebox and the angle of the glass. This causes lots of extra turbulence in the firebox, combine that with the VERY slow burning capabilities, dirty glass results. Small price to pay for 40 hour burns!
The princess has a shallower firebox, therefore tends to have cleaner glass. But can still be gummed up easily with a slow burn and/or wet wood. It still experiences these turbulence issues with the deep floor and the angled glass.
The Sirrico/Ashford does not have a deep belly or angled glass, therefore reducing the turbulence greatly! This allows the air wash to work more effieciently. But the cost is shorter burn times. Only 30 hours or so.