My Glass Jar Turns Black Around the Rim After Every Long Burn — What Should I Test Before Approving the Candle for Sale?

What a long burn does to the flame

In a short session the wick is close to its trimmed length, the pool is still forming and the glass is cool, so even a strong wick can look clean. Every extra hour shifts the balance. The pool deepens and warms, so the wick is fed more fuel. The wax surface drops, so more wick stands above it unless it burns away as fast. Carbon that the flame doesn't burn off collects on the tip as a cap, which behaves like a bigger wick. The jar warms, the room warms, and the evening's fan or AC goes on. A flame that was inside its comfort zone at hour two can be past it by hour four or five, and the soot it then makes rises with the hot plume and settles on the cooler glass at the rim.

"After every long burn" is a useful detail. It means the wick has no margin at that session length, from the top of the jar, not only near the end. If the marks appeared only in the lower jar, the explanation would lean on depth and heat build-up, which is the late-jar soot hub. If they appear only when a fan is on, it is airflow (fan or AC soot with a correct wick). Here the trigger is duration, and the approval question is: at the longest session you will tell customers is fine, does the rim stay clean?

Why the rim blackens: the causes, ranked

Ranked by how often each explains rim soot that follows long burns (our judgement), with the test that separates them. The rim-soot attribution method across wick, load and duration is covered in depth in black soot around the rim; this table is the short version you need before designing the approval test.

Cause 5 is a tendency, not CSI data: vanilla-rich, resinous and dark gourmand oils, higher loads and heavy dye commonly build more carbon; no CSI oil or dye page gives soot data in the text we captured. If your blackening is scent-specific, run the approval test per scent; the per-fragrance posts in this cluster (8% to 10%, vanilla against lavender) set those up. If you can't tell whether the soot is from burning or from blowing the candle out, snuff smoke or burning soot separates them.

The rim-photo and white-card method

Two records do the work. The white card catches soot in the plume while the candle burns, before it reaches the glass. The rim photo and tissue wipe record what the customer will see. The full photo standard (lighting, angle, file naming) is the photo-every-burn post; here is the minimum for an approval test.

Over a full test that is a lot of photos: at about 7 sessions per candle, the six approval candles alone produce about 42 rim photos. Name each file with candle, wick and session (for example A2-S5) so the grid in the diagram builds itself.

The pre-approval test plan and the pass rule

The test 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; keep your own fill if it differs and scale the grams. Two arms, three approval candles each, and one margin candle per arm: 8 candles.

Care instructions: a complement, not a cure

Once a wick passes, the label is how your test conditions reach the customer's table. Common care-label guidance, which you should only print if your test supports it: trim the wick to about 5–6 mm before each burn; burn for no more than your tested session length; keep the candle away from fans, AC vents, open windows and draughts; never leave it unattended; stop using it when about 1 cm of wax remains. The margin candle tells you how firm the session line needs to be: if it marked the rim from its second 6-hour session, "burn no longer than 4 hours at a time" is a line your evidence supports.

What a label can't do is fix arm A. If your current wick blackens the rim inside the session length you would print, the label is asking customers to compensate for the wick. Some will trim and time their burns; most won't, and the rim will be in the photo they send you. Soot only after several hours: wick or instructions first? weighs that trade-off; the short version is: fix the wick to pass at the session you'll print, then print it. If a customer still sends a black rim, the customer-photo questions are the next step.

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 of 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. Rim soot on long burns often needs a smaller correction than a whole rung; if arm B passes on the rim but tunnels, try a lower load on your current wick, or ask us on WhatsApp, and we will tell you plainly if we have nothing in between.

Argued against our own interest: if arm A passes when you keep to 4-hour sessions and the marks only came from five- and six-hour evenings, the fix is the label line, not a wick, and your purchase is a sticker roll. 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. Stepping C2 → C1 saves ₹3.54 a candle: never the reason.

The step to production quantity

Production wicks = candles × wicks per candle × (1 + a defect allowance). Worked example, labelled: 350 single-wick candles a month with a 2% allowance is 357 wicks. If arm B passes on C1, buy 3 × 100 + 50 + 20 = 370 for ₹2,183.00; if it passes on C2, 360 C2 wicks are ₹3,398.40. One 500-sticker care roll (₹413.00) labels the month with 143 to spare. Reorder point = daily use × your lead time + safety stock; CSI publishes no lead times, so ask on WhatsApp. Keep one candle from each production batch for a single 4-hour session and a rim photo: it is the cheapest early warning that a wick or oil lot has changed.

What to buy, and what to skip

Four items for the approval test and the label that follows it, 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: the sticker roll until a wick passes; any 500- or 1,000-pack before three candles per arm reach the floor; 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.

Frequently asked questions