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From: stolfi@magic.DEC.COM (Jorge Stolfi)
Newsgroups: net.misc
Subject: Re: Bottle colors
Message-ID: <897@magic.DEC.COM>
Date: Tue, 15-Jul-86 15:01:17 EDT
Article-I.D.: magic.897
Posted: Tue Jul 15 15:01:17 1986
Date-Received: Wed, 16-Jul-86 07:10:25 EDT
References: <443@valid.UUCP>
Reply-To: stolfi@magic.UUCP (Jorge Stolfi)
Followup-To: net.misc
Distribution: net
Organization: DEC Systems Research Center, Palo Alto
Lines: 47
Keywords: beer, bottle, glass, color
Summary: Brown and green are the colors of iron

John Oswalt wrote in <443@valid.UUCP>:

>   Why is is that beer bottles are sometimes brown, sometimes
>   green, and sometimes clear, but never blue or red or anything
>   else?  

(-: Ahhh, at least, a completely irrelevant question in net misc! :-)

Anyway, here is my $0.00000002 guess:

  Glass colors are usually due to dissolved metallic salts.
  Iron is a common impurity in sand, and threfore in cheap glass.
  There are two main types of iron salts, ferrous (Fe++) and ferric
  (Fe+++).  The former are usually green and the latter are usually
  orange-brown.  Which you get depends on how much oxygen is available
  when the glass is melted.  Therefore, cheap glass has either a
  greenish or a brownish tinge.  
  
  It is possible that bottle makers pour in more iron on purpose to get
  stronger colors, partly for aesthetics, partly to protect the
  contents from sunlight, (-: and possibly to hide occasional yuccky
  stuff on the bottom, roaches, etc.  :-).  
  
  I vaguely remember that manganese salts (purple?  reddish?) are
  sometimes added to neutralize the greenish tinge of ferrous
  impurities.  The result is a slightly dark but uncolored glass.
  (It may also be that brown glass is dark green one with excess
  manganese; I am not sure).  
  
  To get other colors you must add salts of other metals to otherwise
  clear (a bit + expensive) glass.  I am pretty sure the blue ones have
  cobalt.  Copper should give turquoise color, but I don't know if it
  is used.  Uranium (-: non-enriched, of course :-) was once used to
  get yellow.  Also a fine suspension of colloidal gold particles was
  sometimes used for red.  
  
  Hope I got at least some of it right...

   j.