I agree with Kathy. If you want the wax to paint foundation or attract swarms, anything will work, in fact that dark comb smell is what bees like the most. If you are rendering wax to use for yourself though, I find the black comb just doesn't generate enough to be worth the effort. As Kathy said, every single pot, spoon, bowl, etc. MUST be dedicated for use with wax only, because the stuff is literally impossible to clean off. What I do to melt wax is break up my wax into smallish pieces, and tie it all up in some cheap cheesecloth. Then I fill up my crock pot (which is only used for this) with water, put the bag of wax in it, and put it on low for several hours. The wax will melt out of the cheesecloth, leaving the slumgum (the bee parts, used cocoons, and baby bee poop) in the cheesecloth, which can then be removed with a tongs. Throw out the cheesecloth, turn off the crock pot, and the wax will solidify on top of the water. As Kathy said, cheap utensils, bowls, and even crock pots, can all be found at your local thrift stores.
If you want drawn comb to use in your hives long term (i.e. you aren't just trying to get the oldest blackest stuff to attract a swarm), try to go for frames that have yellowish (basically light brown or lighter) wax. Older comb can harbor pesticide or miticide residues, and of course, be sure to at least freeze the comb first before giving it one of your hives. Drawn comb is gold for helping a bee colony grow, since it takes the bees eating 8 pounds of honey to make 1 pound of wax.
