Thanks for your help, Eric.
It was natural veg tanned leather.
I dipped the bottle in molten wax rather than using the oven. I did it very much as you described.
I wonder if I may not have had it in the wax long enough - I had made a previous bottle and it went like crispy bacon, so I was concerned that the second one didn't go the same way. It could have been that I had the wax too hot and didn't leave the bottle in long enough for the wax to penetrate all the way through.
In future I will not have the wax so hot (I like your bain marie idea) and leave it in a little longer.
Maybe that was it?
Cheers, once again.
OK, that sounds like it could be the problem. Honestly, a double bath is essential. You want to melt the wax but keep it at the boiling point of water, and no hotter. As a guide to how long to keep it in the wax, the best indication is the bubbles that come to the surface.
The hot wax will expel the air in the leather. When there are no more bubbles, the leather is saturated with wax. For a flask, or tankard this can take four or five minutes. many people just dunk it in and whip it back out. It doesn't work that quick.
In fact, because you are controlling the temperature of the wax with a bain marie (double boiler), you can leave the leather in there for ages without fear of it "cooking".
I dropped a shot cup off the old wire chip scoop I use to imerse these and it sank to the bottom. I left it there while I dipped all the rest, did three tankards and some leather tablet weaving cards. I fished it out about forty minutes later and it was perfectly fine. When they were all wiped, dried and polished I couldn't tell which one had been in there the longest.
Eric