How much can I reuse paraffin to wax to my chain? I've been waxing my road and mountain bike chains for a few years now, and have always used just paraffin wax.  Typically, I leave the leftover melted wax in the heating element (an old slow cooker) for use the next time, so the wax that's in there now has been heated up and cooled off several times now.

I've noticed that early on when the chain had cooled off it was incredibly stiff with wax, whereas now it's still stiff but much less so.  I'm wondering if the age or constant heating/cooling of the wax is producing a worse/different lubrication.

Should I completely replace the wax every time, or just more frequently, instead of repeatedly re-using it?
Paraffin wax is not a single chemical, rather it is a mix of alkanes with the formula CnH2n+2, having between 20 and 40 Carbon atoms. Commercially available Paraffin wax may also contain additives to raise melting point (normally 37 °C, 99 °F) or reduce brittleness (often stearic acid as found in tallow).

It's possible that when you immerse your chain, the longer alkanes are more likely to be retained in the chain. The stearic acid molecule (C17H35CO2H) is only 18 Carbon atoms long, but the O and OH groups may increase the chances of it adhering to a surface.

Alkane cracking might also be occurring, catalysed by some impurity in the pan or chain, breaking the longer molecules up into shorter alkanes. Paraffin's density should be about 0.9g per ml. Alkanes from C5-C16 (inc octane, decane) are liquid at 20 °C with density 0.63 to 0.77 g/ml. The shortest Alkanes are gases: Methane, Ethane, Propane, Butane. With an accurate scale you may be able to detect a difference in volume between your used wax and the same volume of fresh wax.