What forces a retest
Updated
A burn test describes one system. Knowing what invalidates it is what keeps a growing range safe.
The rule
If it changes the wax, the fuel, the wick or the vessel, the test no longer describes what you are selling.
The test is per combination: wax, fragrance, load, dye, wick and vessel. Six variables, and moving any one of them makes a new system.
Always
A new fragrance, including one from the same supplier in the same family. Oils differ in viscosity and in how they burn.
A new vessel size or shape, because diameter sets the wick and the walls set the heat.
A change of wax, including a new formulation of the same product line.
A change in fragrance load, even by a percentage point.
A change of wick series.
The ones people think are safe
The same fragrance at a different load. More fuel, different flame.
Adding dye, or changing its amount. Dye is a solid the wick has to cope with.
A new lot of the same wax. Natural waxes vary between lots, and a supplier reformulation frequently arrives with no announcement.
The same vessel from a different supplier. A nominally identical jar can differ in wall thickness and diameter.
A vessel in a different color, which can mean different glass.
Building it in
Keep a table of tested systems with the test number against each, and make "does this need a retest" a required question in any change.
The failure mode is never a decision to skip a test. It is a year of small reasonable substitutions after which nothing being sold matches anything that was tested.