My New Wick Gives the Same Melt-Pool Diameter but Produces More Mushrooming — Should I Consider It Equivalent?

What “equivalent” has to mean

The melt pool is the line most makers look at first, because it is easy to see and it answers the question that drives most wick choices: does the candle melt to the edge? It is a good first check. It is also only one of nine lines that together describe how a candle burns, and it is not a proxy for the others. A new wick can reach the glass at exactly the same moment as your old one while burning with a taller flame, a hotter jar, a deeper pool, more soot — or, in your case, more mushrooming. The standard for a replacement wick in a commercial candle is not "matches on the line I checked". It is "no worse than the approved control on every line".

Two lines of that table are filled in: one match and one fail. That is already enough to answer the title question. A wick that mushrooms more than your control is not equivalent, whatever the other seven lines turn out to be. What further testing can tell you is how much worse, whether it matters in a customer's hands, and whether anything else is also different — which decides whether this wick is merely "not equivalent" or "not usable".

What mushrooming is, and why a new wick can cause it

Mushrooming is the build-up of carbon on the tip of a burning wick, forming a small cap that looks like a mushroom. It is commonly described as a sign that the wick is taking up more fuel than the flame burns cleanly at the tip, or that the tip is not being consumed as fast as the wick is exposed. Many things can contribute: a heavier or differently braided wick, a wick that does not curl and self-trim, a fibre or treatment that carbonises differently, and components in the fragrance or dye. Some mushrooming is common and not in itself a defect. The point for a wick swap is not whether your candle mushrooms at all, but whether the new wick mushrooms more than the approved control in the same candle.

That matters commercially for three reasons. The next flame is bigger: a carbon cap left on the wick can make the flame taller when the candle is relit, until the cap burns off. Debris: caps can crumble into the pool or onto the wax surface when the candle is snuffed, which customers notice and dislike. Soot: heavy mushrooming often comes with more smoke and blackening on the glass. None of these show up in a melt-pool diameter reading, which is why a wick can match on pool and still produce complaints.

Why the same pool diameter can hide a different burn

A pool diameter is a reading at one moment, usually near the end of a burn, of one dimension. It does not tell you how quickly the pool got there, how deep it is or how hot the glass is. Geometry makes the point. Two pools of the same 7.5 cm diameter have exactly the same surface area — π × d² ÷ 4 = 44.18 cm² — so the fragrance-releasing surface is identical. But if one is 0.6 cm deep and the other 0.9 cm deep (illustrative depths, not measurements), the deeper one holds 50% more liquid wax around the flame: 26.51 cm³ against 39.76 cm³. A wick that delivers more heat can do exactly that — same diameter, deeper pool — and a deeper pool usually means more heat has gone into the wax and the glass.

Mushrooming is often a sign of the same thing from the other end: more fuel reaching the tip than burns cleanly. So a new wick that matches on diameter and mushrooms more is worth checking closely for pool depth, time to full pool, flame height and glass heat. If those are also higher, the new wick is simply heavier than your old one in this candle, and the bigger-flame post has the isolation test. If they match, the difference may be in the fibre or tip behaviour rather than the amount of fuel — still a fail on mushrooming, but a useful clue for choosing the next candidate.

What to retest

The NEW line is the untrimmed relight. You may never have needed it with the old wick, because a wick that stayed clean behaved the same trimmed or not. Once a candidate mushrooms, you need to know what a customer's second and third lighting look like with the cap still on. The pool diameter drops from REPEAT to CONFIRM here only because you already have a first reading; it still has to be recorded on every burn, and lower in the jar it can change.

The ten-candle test: trimmed and untrimmed

Scoring sheet

CSI publishes no numeric limit for flame height or jar temperature, and this sheet sets none. The rule is relative: no worse than the approved control on every safety line — flame, soot, mushrooming, glass heat, end-of-life — and within your jar supplier's guidance and the candle fire-safety standard you work to. ASTM F2417 is a commonly cited US standard; if you follow it, use its methods. Better throw does not offset worse mushrooming.

Deciding what to do

Notice what is not in the table: adjusting the fragrance load, adding a trimming warning or accepting the wick because it matched on pool. Each of those changes the approved candle to suit a wick that failed a line, which is the wrong way round. If mushrooming is also appearing with your old wick in some fragrances, that is a separate formulation question — the approved control is the benchmark for this test, not an ideal clean wick. And if you already own thousands of the new wick, the 5,000-wicks post covers the options honestly.

The priced test kit

Ten 200 g candles in Luxury Soy Wax Chunks with Sandalwood Fragrance Oil at 8%, plus a 5% pour-loss allowance (a labelled working assumption). The Eco Thin C1 10-pack covers the five new-wick candles with spares; the five control candles use your remaining old wicks. If your production wax, oil or jar differs, use yours — the only difference between groups should be the wick.

The Sandalwood comes out as 1 × 100 g + 1 × 50 g + 2 × 15 g (₹960.52) — cheaper than two 100 g bottles (₹1,005.36) for this 168.0 g need. Sandalwood is ₹5.43 a gram at 50 g and ₹5.03 at 100 g, so the 100 g is the better rate; the small bottles just close the gap without buying 20 g you do not need. Labour, electricity and time are not included.

Recording the result

Write the verdict against the wick, the candle and the date — "New wick X: pool matched, mushrooming 2 vs 0 trimmed, 3 vs 1 untrimmed; not equivalent in 200 g Sandalwood / Chunks". Keep the tip photos with the sheet. Add the wick to your approved-materials list as tested and not approved for this candle, so nobody buys it later as a like-for-like substitute. If a later candidate passes, record which lines it matched and on what dates, update the recipe card, and keep ten wicks and one finished candle from the first production batch as retained samples. The replacement-documentation post shows how to write this so that someone joining your business next year understands why the wick changed.

Related wick changes: if the new wick looks identical to the old one, the same-length post shows the bench checks that can explain a mushrooming difference; if it burns cleaner rather than dirtier, the cleaner-but-smaller post covers the opposite trade-off; and if it is a lighter wick, the size-down post explains why its problems appear later. If this wick is used across several fragrances, the eight-fragrances post shows how to group them. The full wick-change checklist lists every combustion line, and the storage-testing post explains why a wick-only change rarely needs new storage tests.

Frequently asked questions