working with a hothead and MAPP gas

[janetmpete]

I am using a hothead with MAPP gas.  I am new to lampworking and have only taken two classes that of course were taught with Oxygen and Propane.  When I try to use white I get black streaks in it?  What can I do to prevent this?

[Redhotsal]

You are working too low in the flame and maybe the flame is too big. You have to go much slower with the hothead as there isn't as much oxygen in the flame mix. A dual gas torch (oxy and propane) gives you much more control over the gas mix but a hothead is fixed in this regard. Working higher up in the flame will make better use of the available oxygen. Further down in the flame it is hotter and there is much less oxygen.

You shouldn't be working in the "blue cone" section at all, (unless you're reducing).

The black streaks are the glass actually burning on the surface and because there is no oxygen lower down the glass is being stripped of it's oxides on the surface which will give you a murky colour.

Try going slower and higher int he flame - this should work.

See also Mary's advice on this thread: http://www.frit-happens.co.uk/forum/index.php?topic=8713.0