...and some do not have the magnesium all the way down the wick...
Thanks for that tip. I will have to cut one down to a stub and see if it still relights.
I have tested the ones I bought (nothing special - I found them in the grocery store) and they relight quickly after initially being lit. So that's not an issue. But I did not think to test the tail end of the things to see if the very end of the candles support the re-light function.
These candles are just one tool in my firestarting kit. I have all the standards - matches, BIC lighter, ferro rod, vasoline cotton, commercial fire starters, magnifying glass, etc. Other than testing, I have only used one of those birthday candles once - there was a light wind, certainly not gale force, but the candle worked fine. I think it blew out and relighted once, which was all I needed. I have never gotten around to testing how these candles might work after getting dunked in water. My plan was to just slice off the wet end and get some new wick from under the remaining wax. That may not be the best plan if as you say, the magnesium does not go all the way down. I will have to do some testing. Thanks!