[ Ref. Mills Violano Test Roll in 200329 MMD ]

In relay telegraphy we used to use ordinary miniature wire-ended
neon indicator tubes (as used in pilot lamps) across coils to protect
the controlling contacts from arcing in circuits which could have
either polarity.

These days, voltage-dependent resistors (varistors) with a clamping
voltage about twice the coil working voltage would do the same job.
They are cheap and compact and could prolong the life of Violano rolls.
Although any such device will tend to make the release of the coil
more sluggish, it should not be noticeable.

Best regards,
Phil Fortey
London, UK

 [ At https://www.tiffe.de/roehren/neon.pdf  is a lengthy article
 [ about using miniature neon lamps (e.g., type NE-2) and related gas
 [ discharge devices.  A big chart of part numbers and specifications
 [ is included.  -- Robbie