pondering candle molds

I've been making lots of candles this past month. They're all the same: two-inch-diameter, four-inch-high cylinder mold candles. It's been way harder than it ought to be, because your standard candle mold is crap.

Your standard cylinder candle mold, see, is made of two pieces of sheet steel. One piece is rolled into a cylinder and closed with a crimp seam plus a line of solder. The other piece is a flat square with the corners trimmed off; then all four edges are bent down to make feet, and a tiny hole punched in the middle. The cylinder is soldered onto the flat piece, making a cylindrical chamber. To use the mold, you thread wick through the tiny hole and out the open end of the cylinder, then tie it to a copper rod that will sit on top of the open end. You pull the wick tight underneath, cut it off, and seal the hole somehow (both holding the wick in place and preventing the wax from running out the hole).

Problem number one with this design is the hole in the bottom. No sealing method works adequately. I have tried disgusting gray sticky stuff (doesn't reliably stick to the bottom of the mold, almost impossible to get off your fingers); little bits of foam backed up by washers and knots (the foam's only good for two or three castings, doesn't reliably seal, wastes lots of wicking); little rubber spike thingies (great when they work, but often they just plain fall out); and Scotch tape (works better than any of the above, but still leaks).

Problem number two is cleaning. If the inside surfaces of the mold chamber are not spotlessly clean, the surface of the finished candle will have blemishes. However, the shape of the chamber makes it very hard to clean effectively, especially close to the bottom. And the bottom is the most important part, because that's the top of the finished candle. It doesn't help that very little dissolves wax. I have a bottle of patent wax remover, which is nasty volatile stuff that tends to evaporate before it can be cleaned off, leaving an invisible residue that, yup, makes blemishes on the next candle. One might be tempted to throw the things in the oven and bake off all the crud (which is mostly leftover wax dust) but this is a terrible idea: not only does it not work (you replace wax dust with baked-on carbon particles), but the solder typically used will melt in even a mildly hot oven, destroying the mold. Boiling water doesn't work either, because you can't get a continuous flow through the inside of the mold; it just picks up the wax and redeposits it again. And it can cause the mold to rust. Oh, and being made of sheet steel, the molds have edges that are just dying to give you nasty cuts, usually on the webbing between your fingers as you reach deep within the mold with a wad of paper towel.

Problem number three is air bubbles just under the surface of the finished candle. I'm not sure this is exactly the mold's fault. The bubbles seem to come from dissolved air in the wax. Increasing the pouring temperature helps (as this drives out the dissolved air); so does heating the mold before pouring (this discourages prompt crystallization at the outside of the mold, but I have no reason why that would make a difference). I don't like increasing the pouring temperature, because I have to set the wax pot directly on the stove to do it, which is dangerous — not as dangerous now I have an electric stove, but still.

Problem number four is the wrong cooling pattern. Wax shrinks a lot when it cools; you have to top up the mold a few times after the initial pour. Ideally, the wax would crystallize smoothly, evenly, slowly, and from the bottom up, remaining liquid at the top until the very end; one could then top up the mold with no special effort. What happens instead is, it crystallizes from the outside in, leaving a void in the middle with a thin skin over the top. You have to melt out the skin (I do this with a soldering iron) before topping up, which is tedious. Worse, because the wax has solidified around the outside all the way to the top, you get a discontinuity between the old wax and the new, making a visible line on the surface at the top of the mold (which will be the base of the candle). This is not just just a blemish in a place no one ever looks, it's also a weak point; if you try to carve things on the base of the candle you're likely to have great big chips come off, damaging your design.

Related to this is that the candle base never, ever comes out flat. I have a special widget just for flattening them after the fact. It's a big flat metal plate with a ring-shaped catch basin around the outside, that I sit on top of a pot of boiling water. If you set a candle on the flat surface, the bottom melts away wherever it's in contact, until eventually it's flat. There's two problems with this: first, it's one thing to get the bottom flat, but one also wants it square with the sides of the candle, which is hard to do by eye. My candles typically come out with a degree or so of tilt. Second, the wick (poking through the bottom where one cut it off after removing the candle from the mold) interferes;the best thing I've found is to gouge it out to a few millimeters below the target surface with a chisel, but this of course leaves a divot in the base, which (again) causes problems when you try to carve designs there.

I have vague ideas in my head for better molds. The cleaning problem might be addressed by making the mold in two pieces, say a solid block of metal for the base, with a threaded ring cut that the cylinder piece screwed into. This would force one to make the cylinder out of stamped tubing instead of rolled tubing, but that would be good, because then there wouldn't be a seam to make a ridge on the side of the candle. If the base were thick enough, one could have some sort of clamp embedded in it that would hold the wick, eliminating the need for an unreliably-sealed hole.

An insulating jacket of some kind might solve the uneven cooling problem. It would have to be an odd shape, kind of an inverted cone, to get the right temperature gradient going. Alternatively, one might make the entire mold out of one solid block of metal with embedded cooling-water channels, but this strikes me as far too complicated. Any sort of insulation will of course slow down the process enormously, but I see no way around that.

I don't have good ideas for the troublesome top surface (base). It would be nice if there were some magic way to suspend the wick a few millimeters below the upper surface of the molten wax; then one could simply insulate the top and be done. Ideas? How about the air bubbles, anyone got a magic bullet for that?