Gnuplot: Black and White contour plot

I have the following gnuplot plot embedded in my Latex document:

\begin{gnuplot}[terminal=epslatex,terminaloptions={color size 14.5cm, 9cm}]
 set view map
 unset surface
 
 unset key
 unset xtics
 unset ytics
 unset ztics
 
 set contour base
 set cntrparam levels discrete 2,4,8,16,32,64,128,256,512
 set isosamples 100
 
 splot y**2 + 0.1*x**2 notitle
 \end{gnuplot}
 

The plot is alright. All I want to achive is that the contour lines all have the same style, i.e. line type and the same colour, black if possible.

Thanks for any advices.

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