Contaminants in beeswax are of three types, those that are physically embodied or encapsulated in it, those that are chemically bound to it and those that are of a similar chemical makeup as the wax itself that will mix with wax to form an alloy.
Filtering… is dealt with in detail on the Wax Filtration page. A simple method for filtering dirty brood wax would be to melt it in the presence of slightly acidic water first, then pass it through a coarse cloth like hessian then a fine one like brushed cotton or surgical gauze, it comes out lemon yellow, or a strong yellow, without any bleaching, if the final filter cloth is fine enough. So simple melting in water followed by filtration will get rid of most of the water soluble contaminants and particulate debris.
Commercially, different companies use different methods. Some use a volatile solvent then filter cold. Some melt and then pressure filter. The colour that the professionals achieve comes about by just getting all the particulate matter out. I do not think that they go to any trouble to match the colour batch to batch.
Whatever method of filtration is used it will not remove anything that is chemically attached to the wax molecules. But if microscopic resin beads are added to the filter medium that have a stronger affinity for the contaminants than the wax has, we can filter out the beads and attached trash by the methods mentioned above. This will reduce the contamination levels, but will not totally remove the unwanted molecules.
Washing of dark wax may be performed if the entrapped particles that are causing the contamination, and darkening, are so small that they pass through the filter. Beeswax can be lightened by warming the wax, over water, at just below boiling point (of the water) and then hydrogen peroxide (H2O2) is added, which boils… forming very small bubbles that rise through the molten wax. This “wets” small water soluble particles that were previously suspended in the wax and allows them to separate. There is also a bleaching action as the “spare” oxygen is released. This process needs to be performed in a vessel that has tall sides so that the violent foaming does not cause spillage of wax and water.
If we apply this process to the wax that we suspect may have contamination:-
We have heat that will “drive off” volatile components.
We have a thorough wetting that will leach out water soluble particles.
We have a bleaching action caused by the breakdown of H2O2 into water and oxygen. The spare oxygen at the high temperature may oxidise some of our contaminants and the water solubility of the oxidised material may be greater (or less) than before.
Sun bleaching in a solar extractor will lighten the colour of the wax and the UV radiation may break up the contaminating molecules. The action of melting may help lose some of any volatile contamination.
Dilution by admixing fresh wax that is not contaminated is an attractive method of lowering the overall contamination percentage. This is simply achieved by the bees within the beehive, by using starter strips to get new comb drawn rather than full sheets of foundation. If the top few millimetres of comb is then trimmed off and destroyed when the wax in the comb is harvested then contamination rates will be lower still. To this end I think the only way to get a high percentage of freshly produced wax into comb is to use minimum sized starter strips of 1/4” to 1/2” deep.
Settlement of waxes of other types may occur if the mixed wax is held at melting point or just over for a prolonged period of time. However I think the best bet here is dissolve the beeswax in a solvent that does not dissolve the admixed waxes, such differential solution has a far greater chance of separating the components than physical settlement.
Contamination by PDB Crystals
As far as I can tell… Any such residue will be vapourised in an ordinary solar wax melter. There is the added benefit of a little sun bleaching that will reduce some of the staining caused by contact with propolis and some pollens.
Activated charcoal can be used as a filtration media and will remove many chemical contaminants, however I am unsure if all the chemicals involved can be removed in this manner, nor do I know what residual levels may remain after such filtration.