@RRK
Very interesting theory, this would certainly make sense. I remember when I used to start up my 400W diazotype MH lamp that it would flash a lot before finally stabilizing. I first thought maybe it was just particular to that lamp, but I haven't had any other MH lamps to compare it to so maybe they all do that. Interesting

My idea is MH lamps typically have some amount of halide salts condensed on the electrodes. When the lamp attempts to ignite, these salts evaporate immediately and  fill the arctube with metal and halide ions. Halide ions seems to be quite good at quenching the discharge, likely by intercepting electron avalanches. So you often see when MH lamp flashes first on ignition, then goes out, then makes a few repeated attempts and only then establishes the arc. That way, igniting MH lamps needs some insistence with a dense series of ignition pulses having a certain energy. More, usually a presence of some open circuit voltage with rather low impedance is required to be applied together with ignition pulse series. Certain lamps even need a capacitor of a few microfarades that will discharge to the electrode gap at start to do glow-to-arc, automotive or entertainment electronic MH ballasts or ballasts for short-arc mercury lamps are including this!

Okay, I moved it

This topic has been moved to [WANTED].

https://www.lighting-gallery.net/index.php?topic=18608.0

I am no longer a mod so i cannot move this myself. But if you could move this to "wanted" that is where requests for stuff go. This forum is for stuff you are selling. And I created "Webfinds" for stuff you find listed online like on Ebay and marketplace.

@RRK
I was thinking of possibly making my own switch, or maybe using a multiple pole switch with all of the poles in series to make a higher breakdown voltage.

I did not know that MH lamps needed "high ignition energy", that is news to me. I wonder why this is. If it comes to the point of me having to make my own ignitor circuit, at that point it is probably just easier to just buy the appropriate ignitor.

@Ash
The particular transformer I have is completely magnetic (60hz), just a high leakage autotransformer. I should have mentioned that in the original post.

I have several random ferrite cores that I salvaged from various switching power supplies that I could use for making an ignition transformer, but I probably won't end up doing that.

In addition to what's said

Those transformers work at high frequencies, and the winding have sufficient impedance to support it

Connecting 50/60Hz voltage across its output is equivalent of connecting DC. The wire resistance of the secondary is probably a few kOhm to . With low frequency voltage in the order of ballast Voc or lamp Varc, it may dissipate significant power, possibly enough to be destroyed

Which gets me thinking, can this be overcome with a small capacitor in series (something suitable for the voltage, like a string of 1kV..2kV capacitors and equalizing resistors)

Winding a superimposed pulse transformer can be done with with ordinary ferrite cores of the order of ETD38, but some consideration must be made to insulate parts of the winding which are electrically distanced from each other (the wire enamel is not sufficient where turns from different layers may touch)

The fact that the same dirt don't going downward, meaning it is outside the arctube wall rather than inside.

I have a 70 MH lamp (GE if I remember right) that has the same inside...I always just assumed it was halide salts deposited on the glass when it cooled after running.

Getting a good high voltage switch capable of a few amperes of a HID lamp combined with >5kV withstanding and reasonably fast working is possible but not easy.

Also, while this may work for some lamps having low ignition energy like HPS, many lamps need a certain relatively high ignition energy and some OCV voltage presence with a low impedance at the same time to do glow-to-arc, likely this applies to metal halides.

Much easier is to wind your own superimposed transformer or borrow it from something that is not potted, like 150W electronic ballasts. Two or more of  identical transformers can be run in parallel for higher current. A primary of the ignition transformer can be driven by some trivial means (spark gap, SIDAC, etc)