How Much Soot Is Acceptable During a Commercial Candle Burn Test Before I Reject the Wick Configuration?

Why there is no number to look up

Your question, restated: you are running a commercial burn test, some candles leave a little grey on the card or the rim, and you need a line between "acceptable" and "reject this wick configuration". The honest answer starts with what isn't available. CSI publishes no soot data for any wick, wax or oil, and no CSI page states a soot limit. We know of no candle soot limit we could point you to with confidence, and we won't invent one. Soot is also hard to measure without laboratory equipment: what a small maker can do is observe it consistently.

That isn't a weakness of the method; it's what many in-house quality standards look like at the start. A standard is a written, repeatable judgement: what you look at, when, how you grade it, and where the line sits. Its value comes from being applied identically to every candidate, so that "wick B passes, wick A fails" means the same thing in October as it did in July. The wick-page claims you'll read ("minimal soot or smoke" on our Eco wicks, "reducing smoke and soot buildup" on our trimmer page) are claims; your grade sheet is the evidence for your jar and formula.

This post sets the line. The method of photographing the evidence (light, angle, file naming) is the photo-every-burn post; the pre-approval test design with margin candles is the black-rim pre-approval test. For the parallel question about carbon on the wick itself, see how much mushrooming is normal.

The grade scale: smoke, card and rim

Visible smoke is binary and overrides everything: a trail or puffs rising from the flame during a 30-second watch in still air is a fail, whatever the cards say. The white card catches soot in the plume while the candle burns, before it reaches the glass; hold a plain white card briefly well above the flame, never touching it, at the same height every time. The rim records what the customer sees: grade it once the candle has cooled, and on dark, amber or matte glass wipe a fresh white tissue once around the inside rim and grade the tissue, because a thin film can be invisible in a photo of dark glass.

Why grade both card and rim? Because they disagree in useful ways. A card that is grey at hour 4 on a candle with a clean rim is an early warning: the rim will follow in a few sessions. A rim that marks while the cards stay clean often means something happened between checks (a draught, a burn longer than the test, extinguishing smoke), and extinguishing smoke versus burning soot explains how to keep that out of your grades: extinguish test candles the same gentle way every time.

Calibrating the grades before you trust them

Words like "faint" and "distinct" drift. Before you grade a real test, make a physical reference set so that every grade has an example you can hold next to the card in your hand. The quickest way is a calibration candle that soots on purpose: one candle of your formula, labelled as a worked example at 150 g at 8% = 12 g fragrance + 138 g wax in a clear jar, with the wick deliberately left long (untrimmed, say 12–15 mm) and a fan nearby for part of the burn. Hold fresh cards over it for different lengths of time and keep the ones that match grades 1, 2 and 3. Photograph the rim after each short session as it darkens. Then label and date the set and keep it with your test sheets.

Applying the grades across three replicates

Each wick configuration (wick, jar, formula) gets three replicate candles burned to about 1 cm from the bottom, with the jar marked into top, middle and bottom thirds. For each candle and third, record the worst grade seen in any session that burned through that third: 9 cells per configuration. Then apply the tier you chose before the first burn.

Why allow anything in the bottom third? Because heat builds as the wax level falls and the flame sits lower in a warmer jar, so a faint mark late in the candle's life is common even with a sound wick (the late-jar soot hub explains the mechanism). Why only one candle in three? Because if two of three show it, it isn't an outlier; it's the configuration. And why never average? Because averaging lets one black jar hide behind two clean ones, and the customer who gets the black one doesn't average anything.

Reading it. Arm A (current wick): A1 reaches grade 3 in the bottom third, and A1 and A3 are at grade 2 in the middle third. It fails twice over, at any tier. Arm B (one CSI rung down): nothing above 1 in the top and middle thirds, and grade 2 in the bottom third of one candle only (B2). It passes the commercial tier and fails the strict one. That is a business decision, not a grading one: either accept B with a firm burn-time line and an end-of-life instruction, or keep looking for a strict pass (a lower load on wick B, for example). Grading told you exactly where the decision is.

What a failing grade pattern points to

When a configuration fails, don't just step the wick down: look at where and when the grades rose. Ranked by how often each pattern explains a failed grade sheet (our judgement); signs are common observations, not CSI burn data.

Cause 5 is a tendency, not CSI data: vanilla-rich, resinous and dark gourmand oils, higher loads and heavy dye commonly build more carbon, and no CSI oil or dye page gives soot data in the text we captured. Each pattern has its own post in this cluster; for a long-burn-only pattern, see soot only after four hours, and for running the whole chain in order, the systematic soot diagnosis. The rim-soot attribution method across wick, load and duration is black soot around the rim.

The graded test plan

The plan uses the series' default test candle, labelled: 200 g at 8% = 16 g fragrance + 184 g wax (load as a percentage of total weight), in your production jar. Two arms of three (6 candles: your current wick and one CSI rung down) plus the calibration candle: 7 candles. Burn in 4-hour sessions, a common care-label maximum and the one we use here (labelled), about 7 sessions per candle at a worked-example 7.0 g an hour, to about 1 cm from the bottom. That is roughly 42 card grades per arm, which is why the reference set matters.

Once a configuration passes, grading doesn't stop. A production audit (worked example: two candles a month from production, 24 a year, one full 4-hour session each, graded against the same reference set) catches drift from a new wick pack, oil lot or jar batch before customers do. If an audit candle grades higher than the approval candles did, treat it as a new test, not a bad day (the customer-photo replay uses the same logic for complaints).

The CSI buy list and the step to production

CSI's sized, tabbed wicks are three rungs: C1 → C2 → Cotton Braided. Arm B is always one rung down: 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 B grades clean but tunnels, the finer adjustment is on the formula side (a lower load on your current wick), or ask us on WhatsApp; we'll tell you plainly if we have nothing in between.

Argued against our own interest: if your current wick meets the tier you chose, the right purchase is nothing, and a cleaner-sounding wick from anyone, us included, is a formula change you'd have to grade all over again. And because C1 (₹5.90), C2 (₹9.44) and Cotton Braided (₹12.00) cost the same per wick at every pack size, a bigger pack buys stock, not savings; the C2 → C1 step saves ₹3.54 a candle, never a reason in itself.

The step to production quantity

Production wicks = candles × wicks per candle × (1 + a defect allowance). Worked example, labelled: 600 single-wick candles a month with a 2% allowance is 612 wicks. If arm B passes on C1, buy 500 + 100 + 20 = 620 for ₹3,658.00; on C2, 620 for ₹5,852.80. The 500-pack is the same ₹5.90 a wick as the 20-pack; it is simply the pack that matches this volume. Reorder point = daily use × your lead time + safety stock; CSI publishes no lead times, so ask on WhatsApp. Write the passing configuration, the tier and the grade sheet into your spec, so that a later wick lot is graded against the same line.

What to buy, and what to skip

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

Skip for now: arm B wicks if your current wick already passes your tier; production packs before three candles per arm reach the floor; the clear jar pack if you have a spare clear jar; and a non-contact thermometer from us, because we don't list one.

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