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  The liquids used in old Geissler tubes gave them an enhanced effect. Some
  tubes can be externally filled in a separate chamber around the vacuum
  tube, to experiment with different liquids.
  Old organic type liquids often lost their color due to influence of (UV) daylight,
  not all are fluorescent.
  Here are some color examples:
  Quinine, a light yellow fluid - bright blue fluorescent,
  Fluorescein - yellow fluid, bright yellow green
  Rosaniline - magenta fluid
  Magdala red or Sudan red - red fluid.
  Aesculin - bright blue (made from the bark of a chestnut tree)
  Harmaline - pink purple (made from tropical seeds)
Coloured glass seals used before 1900
Platinum wire connections
These were used on the earliest tubes until around 1900. The weak wire connection would easily break making use of the tube more difficult, the solution was a metal cap which was introduced around 1890.
Conical cap
To solve the broken wire connections caps were introduced.
These were used by Richard Müller-Uri and Gundelach and perhaps Pressler from ~1895-1920.
One size 14 mm.
Spherical caps
Used by Pressler and Richard Müller-Uri from ~ 1900 until 1940.
They came in different sizes depending on the tube size from 8-12 mm.
Early French cap
age unknown
French cap
Used on tubes sold by Radiguet before 1900.
Cylindrical Cap
Used by E. Leybolds Nachfolger
Can be first noticed in the 1914 catalogue.

Cylindrical cap
Used by Pressler ~1920-1960. Pressler introduced these as "reinforced electrodes". There are a two sizes 12 and 15 mm.
Conical Cap
Used by NEVA from ~1946
Cap used by VEB Narva
(former Pressler) ~ 1950-1970. These caps are equal on the ones used on common radio and tv tubes.
  Glass seals
  A small layer of lead glass sealing around the metal electrodes solved
  a sealing problem, it was called "einsmeltszglas".
  Probably to distinguish the lead glass in the production from the soda
  lime glass which was used for the tube, the tiny bit of lead glass was
  colored blue (with cobalt oxide pigment) but also red or green is known.
  Platinum wire was used due to the similar expanding coefficient as the
  The early tubes were made of soft soda lime glass, there were differences
  in composition (impurities) due to their local origin. German, French and
  English glass was used. There were many glass sorts like Crystal, Kali,
  Duran and  Berliner glass. German soda lime glass fluoresces apple
  green at an (X-Ray) high vacuum.
  Old English lead glass fluoresces pale blue. (it was a higher quality)
  Didym-Cer glass fluoresces red, uranium glass fluoresces green.
  In many cases the colored glass Geissler tubes came from France, most
  of them made around 1920 and sold by companies like Radiguet.
  Glass of the old antique tubes has often impurities and is very thin and
  delicate with thin electrodes.

  Uranium glass
  Also called Vaseline glass was widely used in Geissler tube production, it
  contains uranium salts (uranium dioxide) this is a natural product, when
  added to glass it gives a nice green color. Under UV and influence or
  electrical discharges the glass fluoresces brightly green. This is
  caused by the radioactive nature of the salt. The measurable radioactivity
  is not harmful for normal use, unless you eat it (not recommended)
  The Scientific Instrument Society has published a paper, Uranuim Glass
  and its Sientific Uses by Paolo Brenni. PDF 1Mb

Green fluorescence of X-ray tubes
  The green fluorescence effect of the glass wall of early X-ray tubes was
  used by doctors to get a rough indication of hardness of the tube.
  Glass makers added some manganese dioxide to reach this effect, the
  more Iron in the glass composition (as an impurity) the more manganese
  dioxide must be added. This procedure appears to impair the working
  qualities to some extent (in respect to it's behavior in the flame). Glass
  made from pure materials shows almost no fluorescence except a pale
  gray blue color. [Herbert Jackson Nature 1915]
All about age, used materials and makers.
Conical cap
10 mm German ~ 1900
Spherical cap
Used by Pressler from ~ 1910 until 1940.
Cylindrical cap
German, size 9 mm ~1920
Cylindrical cap
15 mm ~1920
  End caps and electrodes
  The electrode connection is often the most reliable age mark. Although there are
  pictures in a French catalogue from as early as ca1880 showing tubes with caps
  but most of the oldest tubes which date from around 1860 to 1900 were equipped
  with platinum wire loops connections, sometimes sealed with blue or red or green
  lead glass which gave a durable seal and prevented cracking when the tube cooled
  down in the production process.
  The expensive platinum wire was replaced around 1913 by cheaper Platinum
  coated wire and around 1924 by copper coated wire, both were called Dumet wire 
  (dual metal).
  From around 1935 larger nickel plated cylindrical end caps were used. The 
  youngest tubes have end caps similar to the anode cap on regular radio tubes.
Glass seal connection
Used for a short time by E Leybolds Nachfolger and Gundelach from ~1905-1930 on a few types of Crookes, Geissler and X-ray tubes.
Can be blue or white glass.
Different Fluorescent liquids in a showcase sold by Max Kohl, produced by Pressler.
From left to right:
Aesculin, Eosine blue, Eosine yellow, Fluorescein, Harmaline, Magdala red, Rosorine blue, Rhodamine
The Stands
Early German or French
Probably Geissler Nachfolger,
Franz Müller or Biloret&Mora
ca 1860-1900.
Early German
Geissler Nachfolger Franz Müller and Müller-Uri.
Early English and German style stand

Richard Müller-Uri
Emil Gundelach
past WWII
Tube stands
  Stands if available and original can say something about maker, seller or time scale. For some unknown reason
  they seem to vanish in a lot of cases, often new stands were made for the tubes, or worse, were changed between
  the tubes. There are some typical models which can point to their maker, these can be found in the old
  catalogues. Despite the differences in size all models from the same source are more or less the same in outline.
  The oldest English and German models until ~ 1900 are quite simply turned, black lacquered and containing a
  lead ring in the bottom for stability, the old French models are more prettily turned. Around 1900-1920 Müller-Uri and/or
  Emil Gundelach made very nice turned stands, sometimes even mahogany. Industrial progress can be seen with the
  stands made by Pressler, these are nice looking but in fact simple lacquered beach wood stands, the latest types
  are simple tapered models.
Early French
Early French
Early German
Geissler Nachfolger Franz Müller  Müller-Uri / Emil Gundelach.
Richard Müller-Uri
Emil Gundelach
  Dating tubes is a difficult thing because in almost all cases there is no label of the 
  maker available on the tube. Universities who had their own glassblowers often made
  their own tubes for research on request.
  I did extensive research studying University collections and many books and
  trade catalogues. I found that many trading houses used the same drawings
  (for many years) which indicates they bought from the same glassblowers for
  a long time, but this is not a guarantee that the same models were sold.
  Because of the large number of instrument makers from the past 150 years and
  minimal lecture to compare precise dating and producer information will be still a
  rough guess.
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Replica cap used on tubes from the 1998 "Pressler collection"