[pstricks] "liftpen" in pscustom

[Zbigniew Nitecki]

I am trying to craw (in 3D) an annulus colored in.  Here is my code:
***************************************************************************************
	\begin{pspicture}(-2,-2)(2,2.5)
		\pscustom[fillstyle=solid, fillcolor=lightgray]{
			\parametricplotThreeD[liftpen=1](0,360){%
				t sin 2.24 mul t cos 2.24 mul 0%
			}
			\parametricplotThreeD[linecolor=gray,liftpen=1](360,0){%
				t sin  t cos 0%
			}		
		}
		
\end{pspicture}
*******************************************************************************************
which yields the picture in the attached pdf:

My problem is the line joining the inner and outer circles, which I  
don't want.  I am confused about (1) which value for liftpen would  
accomplish this and (2) whether it should go inside the
two parametricplot commands or in the outer pscustom command (in the  
example above, it is inside the parametricplots, but putting it in the  
settings for pscustom or even all three places seems to have no  
effect) (I've also tried liftpen=2 in these places, without luck).

Zbigniew Nitecki
Department of Mathematics
Tufts University
Medford, MA 02155

telephones:
Office    (617)627-3843
Dept.    (617)627-3234
Dept. fax    (617)627-3966
http://www.tufts.edu/~znitecki/

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