Re: coil discharge color

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John Philip Sanderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <John.Sanderson-at-eng.monash.edu.au>

> Original poster: "Eleanor Flood by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <eflood-at-bellsouth-dot-net>
> 
> Some days ago there were postings on this...I missed copying the very
> one I wanted....a mixture of borax and something to give a green 
> color.I'd like to try
> for another color on a new JL.   Have one with NaCl paste to make
> orange, tried MgSo4 for blue....didn't work.  Any other common
> substances that will give me another color?
> Thanks,  Elli


Dear Elli, 

I caught some of those posts too, but didn't have time to add my own 
comments then and there.  So now for the record... my $0.02:

(1) colour agents:
Ethanol and boric acid should give green.  But it will burn on its own 
once ignited, which sort of defeats the purpose of using it on a JL.  
However,  many other metal salts can be used as colour agents.  If 
you're trying pastes on Jacob's ladder electrodes, you could also try:
copper salts (such as sulfate or chloride) for green
strontium or lithium chlorides for red
potassium chloride for purple
lead sulfate (possibly) for blue... not so sure about that one.
calcium chloride for orange

Note: I haven't tried any of these in this sort of situation myself, I 
would actually be very interested to hear your results if you do try 
such materials on a JL.  

(2) Chlorine donors:
Note that in pyrotechnic chemistry one of the secrets of good strong 
colours is to add a "pinch" of a chlorine donor such as finely powdered 
PVC.  However, there are many differences between a HV discharge and a 
pyrotechnic flame.  I suspect in the case of HV, a drip of liquid 
chorine donor such as dichloromethane or trichloroethane in the paste 
might have more success..(?) But go easy on the quantity, you don't want 
your colour pastes to burn on their own. 

(3) You need colour agents in the right places:
The problem with colouring discharges (particularly Tesla coil arcs and 
streamers) in this way is there is no good mechanism to transport the 
colour agent from the discharge surface into the path of the arc.  It's 
not such a problem with a JL because there is a lot of heat in the arc 
to vaporise and convect the components into the right places, and the 
arc is smaller (you don't have to get colour agents a metre away from 
the electrode).  
With a TC, however, I reckon the approach might be to get the arc to 
track along an insulating surface prepared with some form of the colour 
agents mentioned above.  Or do something fancy with a jet or atmosphere 
of noble gas.

(4) Obligatory safety warning
Before I get "flamed" (yes, pun intended) may I hasten to add that most 
colour agents and chlorine donors are moderately to severely toxic in 
their solid or liquid forms, and the gaseous byproducts produced by them 
in a flame are likewise quite harmful.  
You obviously don't want the fresh outdoor breeze to mess up your arcs, 
but nevertheless, this sort of stuff should be done in a well ventilated 
space of some sort... be careful of your lungs.
And (you probably do this anyways), download and read the material 
safety data sheets (MSDS) for all chemicals you obtain so that you 
understand the hazards first and can take appropriate precautions.

End of prattle.  Comments welcome... particularly from anyone who has 
tried this stuff!

John Sanderson