Also, I plan to burn these candles continuously. What is the most thrifty way for me to to safely do so? Note that my entire house is carpeted. Buy a gigantic basin or stainless steel rectangular cake pan?
For general candle use, I use flat pottery trivets (that are smooth/have a stable surface) for multiple candles when they're wide enough to be stable without a holder. (As two of yours: a 1.5" diameter that tall, I would probably want something a bit more secure.)
In terms of long-term burning, one option that can work really well is an old aquarium. It doesn't necessarily have to be totally leak proof: if the leak is high on the sides, you can fill it with a couple of inches of water at the bottom. If the leak is lower down, you can fill it with sand (so that if a candle tips, it'll snuff itself out, etc.) Goodwill or other thrift stores might have one cheap.
The trick of course, is that it's not the best choice for a single use thing: you'll need to store it, etc. later. Depending on the layout, you might be able to use something like a deep punch bowl or other large bowl, as long as the burning candle cannot fall with the flame out of the container.
(So, a 2 inch deep baking dish with water in the bottom doesn't work well for a 7" candle: there are directions the candle can fall where the flame might not go out. A 5" deep bowl with a 4" tall candle is just fine.)
One option some people use - if you can block off either your kitchen sink or your bathtub from pets, small children, and any other people who might need to use the space - is to move lit candles to the sink or bathtub when you leave the house or overnight (or any other time you aren't in a regular line of sight to them.)
Frankly, I don't bother with any of those (small house with limited storage space, cat's litter box is in the bathroom, so I can't shut the door, etc.) If I'm doing an ongoing candle spell, I either design it to run over multiple days (designed so I burn an inch of candle a night, for example, which I can do with some planning while I'm home) or I burn it when I'm home, and snuff it, focusing on holding the intention until it's relit. When I'm home again, I relight it, give the intention a little extra energetic push, and let it burn as long as I can.
Important Information about this Archive Board
