I’m Using Two Wicks in a 10 cm Jar but One Consistently Burns Larger than the Other — What Could Cause Uneven Wick Behaviour in the Same Melt Pool?

Why two flames in one pool drift apart

A double-wick candle is not two single candles side by side. Once the pools merge, both wicks draw liquid wax from one pool. Each flame warms the wax around its own wick, and the wax there turns liquid sooner and deeper. If one flame starts a little larger, the wax around it tends to get warmer and deeper; whether that makes that flame grow or its partner drown depends on the wick and the candle, which is why you measure rather than guess. These are tendencies, not CSI data, and they are why a small early difference is worth chasing before it becomes a candle that burns hot on one side.

The geometry is symmetric only when the setup is. In CSI's Apothecary Glass Candle Jar (outer rim about 10 cm by the page, 9.3 cm inside on our 0.35 cm wall assumption, which may overstate the inside of a "thick-walled" jar), the starting spacing this cluster uses is the inside radius, 4.65 cm, which leaves each wick 23.25 mm from the glass along the wick line. Each wick then serves half the pool, 33.96 cm² of 67.93 cm². Move the pair 4 mm towards one side and one wick sits 19.25 mm from the glass while the other sits 27.25 mm away, 42% further. A few millimetres is easy to lose when two tabs are pressed down by hand, and it can be enough to make the two flames behave differently.

That is why this post does not start with a wick size. If both wicks are the same size from the same pack, cut to the same length and set symmetrically, they should behave alike in still air; when they don't, the difference is in the setup, the room or the individual wick, and each of those has its own fix. For the hub's view of pairs in 10 cm jars, start at the 10 cm cluster hub; if the pair leaves a ring at the glass rather than one big flame, the ring-shape reading is in the perimeter-wax post.

The rotate test, session by session

The logic is simple. When you turn the jar 180°, everything that belongs to the candle (each wick, its trim, its position, the jar's own glass) moves to the opposite side of the room. Everything that belongs to the room (the draught, the window, the fan, the sun, and the slope of the table) stays where it was. Watch which way the larger flame goes.

Two cautions. First, a tilted table follows the room. When you turn the jar, the slope under it does not turn, so liquid wax still gathers on the low side; that reads as row A, and a level on the table settles it. Second, row A is not proof of a draught you can feel. Air moving slowly from an AC vent or a fan across the room can lean two flames enough to matter. Mapping the air and the fan-off test belong to the ceiling-fan post; here, row A simply tells you that buying wicks will not help.

The six-point candle checklist

Run every row on the candle you already have, ideally at the end of a session while the pool is liquid and the wicks are easy to see. Write down a number for each wick, not a yes or no. The rows are ordered by how cheap they are to fix, not by how likely they are; we don't have data to rank likelihood, and nobody publishes it.

Reading the checklist

Trim first, always. Unequal trim is one of the causes that can come and go between sessions (carbon and lighting order are the others), and it is often why a test reads as row C. If you trim by eye, the wick you trim second is often the longer one. Cut both, then hold a ruler against each. The Candle Wick Trimmer page says "Trim your wick to 1/4 inch before every burn", about 6 mm, and that is a sensible common target for both.

Pack and size second. C1 and C2 are both pre-tabbed Eco wicks, and side by side the difference in thickness is visible, but on a bench with two open packs it is easy to pick one of each. If you used wicks from two different orders, note which order each came from. CSI publishes no lot data, so if two wicks from one pack burn differently in a symmetric setup, send us photos on WhatsApp; we would rather hear about it.

Lean and position third. A wick that leaned while the wax set puts its flame nearer the glass or nearer its partner. A wick that was pressed down a few millimetres off its mark changes the wick-to-wall distance, and on a 93 mm pool a 4 mm shift makes one wick 42% further from the glass than the other. Measure at the wax surface from each wick to the inside of the glass along the wick line. In clear glass like the Apothecary jar you can also look up through the base and see where each tab sits.

Depth and carbon last. A deeper pool beside one wick is a result as often as a cause: the bigger flame melts deeper. Note it, but if the surface is level and the other rows are equal, depth alone is not a reason to change anything. A carbon cap on one wick (mushrooming) can make that flame larger and sootier; remove it before the next session and see whether the difference goes. If it keeps coming back on one wick only, that wick is different from its partner. Why carbon builds over several burns is covered in the accumulated-carbon post.

The swap twin: wick, jar side or setup

Sometimes the big flame follows wick 1, the trims are equal, both wicks came from the same pack, neither leans, both sit within a millimetre of 23.25 mm from the glass, and the pair is still uneven. Three suspects remain: that individual wick (or its lot), something about that side of the jar, or something in the way your holder sets the pair. One candle cannot separate them, because in a poured candle the wick and its position never move apart. Two candles can.

Setting up the twins

Pour two twins the same day from one melt: same wax, oil, load, fill, jar batch and cure. In each jar, put a pen dot on the glass and mark the two chords 23.25 mm in from the glass on opposite sides. If your original pair came from two packs, or you suspect a pack, use one wick from each pack in each twin. In Twin A, the pack-1 wick goes on the dot side and the holder's marked end faces the dot. In Twin B, the pack-1 wick goes on the side away from the dot, and the holder is turned so its marked end faces away too. Hold each wick on its own centering bar laid along its chord, two bars per jar, and measure both wick-to-wall distances once the wax has set.

The twins answer one more question for free: whether your corrected setup works. If both twins burn evenly, that is two candles of evidence for the setup you will use in production, and they continue to full life as ordinary test candles. The full-life heat questions for a pair are a separate matter; for those, see the double-wick late-heat post.

Grams, wicks and rupees for the twins

The worked example uses the Apothecary jar's 500 gm size at a 500 g fill, matching the cluster hub, with Sage and Cedarwood at 8% of total weight: 40 g of oil and 460 g of CSI 464 per candle, on two Eco C2. That fill is our labelled choice; the page says "Fill capacity: ~500 g - 700 g (2 sizes)" without saying whether that is to the brim, so weigh water to your own fill line first.

One twin costs ₹743.16: ₹278.48 of oil, ₹233.40 of wax, ₹212.40 of jar and ₹18.88 of wicks. Costs are worked examples and exclude labour, freight, packaging and GST. From nothing, the cash outlay is ₹1,840.80 (oil 100 g, wax 1 kg, two jars, a C2 10-pack and a centering-device pack). The rotate test and the checklist, by contrast, cost nothing at all, which is why they come first.

Fixes that hide the cause

Swapping both wicks for a smaller size. If one flame is too big, two smaller wicks may calm it, but the partner, which was already the weaker one, gets weaker too. You may trade one large flame for a ring at the glass on the other side. A size change is a separate, controlled test for when both flames are wrong; the step-down post owns that question for a 10 cm pair.

Trimming the big wick shorter than the other. It works for a session and it hides the cause. If the cause was a draught, your customers' rooms will have different draughts; if it was position, every candle from that setup carries it.

Moving the wicks closer together. Spacing is a real lever, but not for this symptom. Moving a symmetric pair inwards changes both wicks equally; it does not make two different flames alike. Spacing ladders belong to the too-close post and the 9 cm spacing post.

Changing the oil. Both wicks burn the same oil from the same pool, so an oil cannot favour one of them. An oil can change how both wicks behave, which is a different question.

What to buy, and what to skip

Five items, in the order the test needs them, chosen on page statements, price and stock on 29 September 2026. CSI publishes no wick-performance data, so nothing is ranked on burn results. Oil candles are counted at 40 g (500 g fill at 8%) and 12 g (the standard 150 g candle).

Frequently asked questions