Making candle 2,000 match candle 1
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Consistency in this craft is unusually hard, because a candle is a system of six things and any one of them moving changes the burn.
Six variables, all of them drift
Wax lot. Natural waxes vary, and reformulations happen without announcement.
Fragrance lot. Fragrance houses reformulate, sometimes for regulatory reasons.
Load, if weighing is sloppy.
Dye lot, which shows as a shade drift on a shelf.
Wick lot, which is the one nobody suspects.
Vessel, if a supplier substitutes a nominally identical jar.
Any of those is a retest, not an adjustment, which is the discipline that separates this from most crafts.
The reference candle
Keep one candle from every approved batch, cured, lidded, stored cool and dated.
Compare a new batch to it for color, surface and cold throw before the batch goes out, and burn a reference alongside a new one when anything seems different.
This costs one candle per batch and it is the only way to answer "has it changed?" with anything other than an opinion.
Controlling the inputs
Record wax product number and lot, fragrance name and lot, load, dye and amount, wick series and size, and vessel supplier and part number, against every batch.
Ask suppliers to notify you of reformulations, and burn a confirmation candle from every new wax lot before committing the lot to production.
Checking a run
Weigh ten filled vessels and look at the spread, not the average.
Inspect against the reference for surface, color and fill level.
And burn one from the run. Not a full test, but a single four-hour cycle to confirm the melt pool reaches the wall as it did in the approved test. A run that has drifted shows there.