Jig making....been doing this a long time. I made my first jigs in 1965 using an oak mold.
I'll add to this.
Bareknuckle has the right idea for pre-heating aluminum jig molds. I fill all of the cavities, going to be used or not, and let the lead sit in the mold about 20 seconds before popping the castings out. Depending on the size of the jig I may do this ten times or so and this depends on the air temp. On 1/32 heads in January I bring the mold in the house for a day before pre-heating and that mold will get filled at least ten times to warm it and that includes filling the larger heating chambe under the jig cavities. Get the mold hot. If you can't hold the aluminum with a bare hand, then its hot enough.
Wheel weights have a ton of tin and antinomy in them and can be darned hard to cast with especially in the very small jigs. I'd avoid using that metal source for jigs under 1/8. The absolute best lead in the world for casting jigs comes in 1/8" 4X8 foot sheets used in the walls of medical x-ray facilities. Living with the Mayo Clinic and two of its affliated hospitals only blocks away is a bonus for me when they do u-grades to these rooms. Having friends in the construction trades that does the work is the frosting. I'll come home occasionally to find five or six pieces of rolled lead weighing up to 100 pounds laying in front of the garage door. I melt it into two pound ingots for use. Plumber's lead is yet another source of pure lead. Pure lead is easier on the heating elements in your electric hot pots too and for trimming sprues the pure lead can be snapped off, no cutting needed. Snapped sprues leave little evidence while cut sprues always leave a sharp cut edge.
I went to a Hobby Lobby and picked up a couple different sizes of bead pliers. These are used to hold beads while making jewelry and the two sizes I picked up hold jigheads from 1/64 to 1/16 using the smaller plier and up to 1/4 heads in the other. They grasp the head and hold it firmly without denting or mis-shaping the heads while the sprues get snapped off. I make some flathead jigs up to 3/4 ounce and they require no tools at all to trim sprues as long as pure lead is used.
By holding the hook end in a needle-nosed pliers you can slip the lead end just into the hot lead of the pot to get a bad casting off the hook. Don't bank on doing this too many times with the same hook as the temper in the fine wire will change in a hurry. And regarding hooks, buy quality hooks that YOU are satifisfied with. All of the Mustads have done me well over the many years. VMC's, Matzuos, Gamis, and some of the Ditachi's are great hooks to work with as well. The bottom line on the hooks is that if you have trust and faith in them, the whole of what you are doing with casting and all will reflect that. I stay away from Eagle Claws. The gold hooks are brittle in my opinion and the bronzed ones have too much laquer on them. When they get cast the laquer shrinks away from the lead leaving a loose casting on the hook.
I'm going to offer a couple suggestions from an ice angler here since we are talking jigs. Instead of dumping a dozen of one color of a jig and size into an open tray, pick up some jig boxes that allow the jigs to be clipped into place so the can't fall out or rattle around. This is how I manage my small jigs and they stay nice and clean and ready for use without having to untangle 200 jigs to get one. Boxes for jigs to be kept in the fashion just mentioned do well with small jigs but larger ones are harder to deal with. For jigs 1/8 and up I line the bottoms of the compartments holding jigs with 1/4" foam bought at a fabric store. I cover the jigs in those compartments with another pice of foam that is 1/2" thick. When I close the box cover the foam holds those jigs in a rattle-free world. The paint and hooks stay protected this way and will provide you with a lot more service. Nothing is more disgusting than opening a box of jigs and seeing paint chips, rust, curled hook points.....you take care of them, they'll take care of you.
