Metallic paint spark strip

by aturner

 

Another half-baked idea from yours truly.....

 

I once built a launcher painted with gold metallic paint, where the spark would arc across the outside of the launcher instead of jumping the spark gap.

 

As a followup on that experience, I decided to test two metallic paints, and to see if I could replicate that spark. As I've mentioned before, I think this sort of paint just might work as a spark strip.

 

Here's the paint I tried.

 

I sprayed one coat of each metallic paint on a half-section of 1.5" PVC pipe, and waited a few hours for to it to dry...

 

Then attempted to measure the resistance, but got a reading of infinite ohms....

 

And finally, I simply played with this setup and observed the sparks...

 

I was surprised to get an infinite ohm reading. I had expected something lower than that. I took additional readings after the paint had cured, but it was always infinite.

 

Gold versus silver...

The gold paint clearly carried the spark better than the silver. Or perhaps the contrast was better? Or perhaps the spark travels more "inside" the silver paint, and more "on top" of the gold paint? Regardless, neither of these paints yielded sparks as impressive as the original gold painted launcher.  For the sake of simplicity, I then focued on the gold paint as a test subject.

 

I then added paint until I built up three coats of paint.  I was still reading an infinite resistance, I decided to just put some electrodes in my test rig and give it a try. Started off by grabbing some random screws and checking to make sure I still got a good spark:

With that established, I decided to drill pilot holes at each end of the test rig, and wire up the bbq ignitor:

But only wimpy sparks dammit! Same as before, with just a tiny spark around each electrode. I even checked in the dark. Wimpy sparks just will not do!!!

 

So I tried moving the electrodes closer and closer, until I had them close enough that the spark could jump the air gap between the electrodes if it "wanted to".

But got the same result! Just a wimpy spark around each electrode. Again I took the test rig to a dark area where I could more easily observe sparks. No sparks connecting the electrodes on the front or the back of the test rig. But why?

 

So then I removed the electrodes and held the ends of the text leads at the same distance that the electrodes had previously been at. This was to confirm that indeed the ignitor was working, and that the spark could jump this sort of gap across air:

And this worked! But why would I observe a nice bright spark across an air gap, but then only a weak spark across the same distance when the electrodes were in contact with metallic paint?

 

I had to step back and think about this for a moment. Hmmmm. I guessed that when the electrodes were installed in the painted PVC, that the spark must be traveling through the paint, and this was preventing me from observing the path. Just a guess.

 

How to test this guess? Well, if the paint was carrying the spark too efficiently and masking most of the spark, then it was time to create gaps! I thought this would force the spark to the surface. I already had a painted surface, so whipped out my utility knife and etched a cluster of four thin lines that were to serve as gaps between the electrodes. And it worked! Four little sparks across a small gap, which showed the path was not the air gap, but rather the four tiny gaps in the paint. Then I moved the electrodes to the far ends, and began etching additional gaps. Here are six gaps, which were easily jumped:

 

I continued adding gaps and clicking the BBQ ignitor:

I finally got to 26 gaps, and decided this was enough:

 

Finally, here's a photo from the backside, showing that my electrodes were spaced about 11.5 inches apart:

 

 

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