How Do I Distinguish Soot Caused by an Oversized Wick from Soot Caused by Drafts?

Two causes that look alike from across the room

Here is your situation as precisely as we can put it. Your candle leaves soot on the glass. In the room where it happens, the air moves at least some of the time: a ceiling fan, a split AC, a cooler in summer, a window open in the monsoon. The flame looks large and unsettled. You don't know whether the wick is too big for the jar, which is a formula problem you must fix before you sell, or whether the air is pushing a correct wick out of shape, which is a placement problem you should explain to customers. The two fixes pull in opposite directions. Wicking down a correct wick to beat a fan can leave you with a candle that tunnels. Blaming the fan for an oversized wick sends a candle to market that soots in every still room too.

They look alike because both end at the same place: a flame that takes in more fuel than it can burn completely, so unburned carbon leaves as smoke and settles as soot. They get there differently. An oversized wick, commonly, supplies too much fuel to a flame that is otherwise in calm air. A draught, commonly, distorts a flame that had about the right amount of fuel, so parts of it burn badly. These are widely reported tendencies, not CSI measurements, and they are why the test works: remove the air, and only one of the two causes survives.

Two siblings sit right next to this page. If you already know your candle soots only when the flame flickers and you want to know how much air it takes, and what to tell customers, that is the airflow post (6927). If you are confident the wick is right and the question is whether to build in margin for fans, that is the fan-and-AC margin post (6937). This page is for when you don't yet know which of the two you are looking at. The quick, no-cost version of the same question for a flickering flame is in the flicker-or-oversize post; this page adds the full two-arm test, soot position and a confirmation arm.

The signs, one by one: oversize against draught

Each sign below has an oversize version and a draught version. Read them on the same candle, at the same hour, in both rooms. They are common observations, not CSI test data, and you should expect some overlap: a draught can deepen one side of the pool and lengthen a wick, and an oversized wick can flicker on its own in still air because the flame is too big to stay steady.

Sign 5 is the one people skip, and it is the most useful for customer complaints. Soot on one side is a direction: put the jar back where it stood and look at what is on the other side of the flame. Soot all round is no direction, and wind does not do that on its own. Sign 6 is the tie-breaker. In our illustrative worked example, the current wick burned 7.0 g an hour in still air and the next rung down 5.8 g, about 17% less. Your numbers will differ, and only your scale can give them, but a clear gap in still air is evidence the wick is doing more work than the jar needs.

The causes, ranked: burning versus making

Ranked by how often each explains soot that shows up "in a draughty room" (our judgement), with what separates it from the others. The burning causes cost nothing to test; the making causes need candles.

Cause 4 is the one that fakes a draught. An off-centre wick puts the flame closer to one wall, so the pool is deeper on that side and the soot lands there, in a perfectly still room. If arm S shows a one-sided pool, measure the wick before you draw any conclusion. Cause 5 is a tendency only: vanilla-rich, resinous and dark gourmand oils and higher loads commonly build more carbon, and no CSI oil page gives soot or wick data in the text we captured. Cause 6 belongs to the late-jar soot hub (6921). If your soot shows only in the last third, read that first. For the opposite case, a perfect-looking pool that still smokes and mushrooms, the melt-pool-is-not-enough post explains why diameter alone can't clear a wick.

The two-arm test, and the confirmation arm

The test uses the series' default test candle, labelled: 200 g at 8% = 16 g fragrance + 184 g wax (load as a share of total weight), poured in your jar with your oil and your current wick. Luxury Soy Wax CSI 464 is the worked-example wax (page: "Pour Temperature 80°C – 90°C", "Fragrance Load Up to 10%"). Pour all 9 candles on the same day: arms S and D on your current wick, and arm R one CSI rung down. Pouring arm R now costs three candles and saves a week if the verdict is oversize.

Only want the verdict first? Arms S and D alone need 1,104 g of wax: the same 2 × 1 kg (₹1,014.80) and no new wicks. Two 1 kg packs (₹1,014.80) cost less than four 500 g (₹1,040.00). Already own holders? Leave them out of the total.

Reading the result: the decision table

Two things make the table honest. First, in the "oversized or formula" row, arm R tells you which. If one rung down burns clean in still air with your oil and load, the wick was too strong for that jar and that formula. If it still soots, look at the load and the oil before going down again (soot after 8% to 10% and vanilla against lavender set those tests up). Second, a draught verdict is not a free pass. If your customers' rooms are like arm D, the soot will happen in their homes, and a care line has to carry the fix. Whether to give up some melt for a margin against fans is 6937's question; whether a slight draught already counts as "borderline" is 6927's.

The CSI buy list and the production step

CSI's sized, tabbed wicks are three rungs: C1 → C2 → Cotton Braided. One rung down means Cotton Braided → C2, C2 → C1, or a C2 pair → a C1 pair. There is no sized, tabbed wick between C1 and C2 or between C2 and Cotton Braided, no smaller sized, tabbed wick than C1, and one wooden-wick listing with no widths. If arm S soots on C2 and arm R tunnels on C1, you have hit the gap in our range. Ask us on WhatsApp and we will say plainly that there is nothing in between, or try a C1 pair, or make the finer adjustment on the load.

Argued against our own interest: half of the four corners end with no purchase from us. A draught verdict needs a placement line; a not-reproduced verdict needs a conversation with the customer. And if you do step down, C1 (₹5.90), C2 (₹9.44) and Cotton Braided (₹12.00) cost the same per wick at every pack, so a bigger pack buys stock, not savings. Stepping down saves ₹3.54 a candle from C2 to C1 and ₹2.56 from Cotton Braided to C2, a side effect and never the reason.

The step to production quantity

Only after arm R passes on three full-life candles: production wicks = candles × wicks per candle × (1 + a defect allowance). Worked example, labelled: 250 single-wick candles a month with a 2% allowance is 255 wicks. On C1 that is 2 × 100 + 50 + 20 = 270 wicks for ₹1,593.00, with 15 to spare. A 500-pack (₹2,950.00) costs the same ₹5.90 a wick and ties up ₹1,357.00 more cash. If the verdict was draught and C2 stays, 260 C2 wicks are ₹2,454.40. Reorder point = daily use × your lead time + safety stock; CSI publishes no lead times, so ask on WhatsApp. If you later change wick lot or supplier, re-run arm S on one candle before you trust the old verdict.

What to buy, and what to skip

Four items, chosen on page statements, price and stock on 7 October 2026. CSI publishes no soot, flame or airflow data, so nothing is ranked on performance, and each card says when not to buy.

Skip for now: any wick at all until arm S has burned two sessions; Cotton Braided if your jar is 8 cm or narrower and the verdict is draught (its page positions it for jars "exceeding 8 cm"); a new oil "that burns cleaner" while the wick question is open; and a non-contact thermometer from us, because we don't list one.

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