Usually, I make the liquid a bit bigger than the interior of the glass.
Here's a cross-section:

++++ = glass
**** = liquid
#### = both

  |+++++|#|***************|#|+++++|
  |+++++|#|***************|#|+++++|
  |+++++|#|***************|#|+++++|

In other words, the liquid & glass overlap a bit.  Try it and see if
it works.

-Nathan

Margus Ramst wrote:
> 
> Equiprawn > wrote in message <36f03a21.0@news.povray.org>...
> >
> >I might know what this is. If you fill a clear glass with water, and look
> at
> >the top where the water's surface meets the glass, you will see that the
> >surface doesn't stay flat, but in fact curves up slightly. This happens
> >because of water tension, and in fact happens with all liquids, AFAIK. The
> >only exception I know of is liquid mercury, which curves down instead of
> up.
> >
> 
> No-no, that's not what I meant (the whiskey surface actualy _does_ curve,
> BTW)
> I meant that there shouldn't be such a big gap between the inner surface of
> the glass and the whiskey; I have modeled quite a few glasses (and stared at
> them them in Real Life :) and they look different.
> Let's see if I can explain this... Beacause of refraction or total internal
> reflection, the walls of the glass should look very thin, i.e. the colour of
> the liquid should extend all the way to the outer surface of the glass, even
> if the glass is quite thick. The fact that the liquor in my image is so
> clearly separated from the outer surface of the glass gives the impression
> that the glass doesn't refract...
> Hope you undesrtood. If not, feel free pour yourself a drink and check it
> out. It's Black Velvet whiskey, if you want a precise test ;)
> 
> Margus

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