My Candle Uses a Very Thick Glass Jar — Does Glass Thickness Affect How I Interpret Wick Burn-Test Results?

Thick glass changes two readings, not one

Reading 1: the pool is smaller than the outside says

Wick decisions follow the inside diameter, and thick walls shrink it. CSI's listings give outside or unspecified diameters, never an inside one, and no listing states a wall thickness; the series' usual 0.35 cm wall assumption is too thin for a jar sold as thick-walled. Measure with callipers: across the inside of the mouth, and the wall itself at the rim, and write both on the pre-order spec sheet. Why the outside figure misleads is the external versus internal diameter post.

The direction matters for purchasing. Taken alone, a smaller pool points to the same wick or a smaller one, not a bigger one. If you read a 7 cm outside figure as the inside, you plan for 33.18 cm² and test a wick sized for more wax than the jar holds.

Reading 2: the early edge melts late

Glass takes up heat. A thicker wall has more of it to warm, so in the first sessions, before the jar has warmed through, the wax touching the glass commonly melts last. That is a tendency, stronger in cold rooms and short sessions, and it shows as the thing that tempts people to buy up: a thin ring of solid wax at the glass on burn 1 or 2. Later in the life the same glass holds heat, which is why thick-walled and heavy-based jars are commonly judged on the final third, not the first. Thick-base effects on the bottom of the burn are the thick-glass-base post.

The edge-ring rule: why not to buy up yet

Here is the purchase that is easiest to get wrong. Burn 1 leaves a 2–3 mm ring at the glass; the instinct is to order the next rung up, and often a big pack of it. In thick glass that order can fix a problem the wick didn't cause and create one it will: a larger wick that clears the early edge may run hotter in the final third, when the same thick glass is holding heat. The deeper question of whether to increase a wick that tunnels early but catches up by burn 3 is the catch-up-by-burn-3 post; this page owns the step before it, buying evidence instead of wicks.

Session length is the cheapest variable to get wrong. A very rough rule of thumb is about an hour per 2.5 cm of width, about 2.4 hours for a 6.0 cm inside diameter, and a common benchmark for a full first pool is about 3–4 hours; thick glass argues for the longer end. A ring after a 90-minute burn says nothing about the wick.

The control arm: same wick, thinner glass, matched inside

A control arm holds everything still except the glass: same wick, oil, load, wax bag, fill weight, pour temperature, cure and room. The trap is choosing the control by outside size. A thin-walled jar with the same 7.0 cm outside has 17.4% more pool than the thick one, so it would melt to the edge for two reasons at once, and you could not tell them apart. Match the inside instead: here a 0.25 cm wall and about 6.5 cm outside gives the same 6.0 cm inside.

How close is close enough? Our judgement is within about 2 mm on the inside diameter. At 2 mm under, the pool is 26.42 cm² (-6.6%); at 2 mm over, 30.19 cm² (6.8%). Beyond that the control starts testing a different pool.

Why three a side? One candle is one draught or one off-centre tab. Three let an odd candle be outvoted, on each side of the comparison.

What the control arm costs, line by line

Per candle that is ₹115.46 in materials on C2, or ₹209.86 with a CSI 150 g jar, excluding labour, freight, packaging and GST. The control arm itself, the three thin-jar candles you would not otherwise pour, is ₹346.38. If your thick-jar candles are already burning from an earlier pour, you could pour only the three controls, but a control poured on a different day from a different pot is a weaker control; our judgement is to pour both arms together (₹692.77 for six).

If you are tempted to use one of CSI's 7 cm matte or glossy jars as the thin control, check it first: their pages read "Height 8 cm width 7 cm" with no wall thickness, and a 7 cm outside thin wall is exactly the unmatched case in the diagram. At ₹70.80 a jar in a 5-pack (₹354.00) it is not expensive to find out, but measure one before pouring three.

Reading the grid, and the purchase each square allows

The second row is the one the control arm exists to catch, and it usually ends without a purchase: the ring in thick glass often narrows as the jar warms over successive burns (a tendency). If it is gone by burn 3 and the thick candles pass the full life, C2 is approved for that jar and the money you didn't spend on a bigger wick stays yours.

Thick glass has a second half to its story. The heat it held back early it can hold late, so the final third is where a thick-walled jar commonly argues with a wick. Watch the flame and its distance from the glass by eye in the last sessions; safety-first acceptance criteria for a jar that gets hot near the bottom are the hot-jar-near-the-bottom post. If C2 runs hot late, the purchase question becomes a down-rung, not an up-rung: one C1 20-pack (₹118.00) for three candles, the same reserve logic as the narrowing-jar reserve post.

If the wick is the problem: the buy-up order, then production

If both arms ring, the buy-up order is small: the Cotton Braided 10-pack (₹120.00), and three 150 g candles in the thick jar, ₹354.06 in materials. Oil: three more candles need 36 g; the 100 g bottle from the control arm leaves only 28 g, so add a 50 g (₹170.00) or plan the nine candles from the start: 108 g of Citrus Lemon (100 g + 50 g, ₹470.00, leaves 42 g) and 1,242 g of CSI 464 (1 kg + 500 g, ₹767.40, leaves 258 g). Per candle, Cotton Braided adds only ₹2.56 over C2 (₹118.02 against ₹115.46); the cost of the buy-up is the candles and the days, not the wick.

Once one wick passes the full life in the thick jar, three candles of three, size the order by the formula: wicks = candles × wicks per candle × (1 + allowance). At 200 candles a month and a 5% worked-example allowance, that is 210 wicks.

Set the wrong wick against that month and the control arm looks cheap. Two hundred candles poured on Cotton Braided at production prices are ₹23,201.04 in oil, wax and wicks, plus ₹18,880.00 of CSI 150 g jars, all exposed to a final-third failure that a ₹346.38 control arm and a full-life test could have flagged. What waiting for full life costs against a wrong bulk order, in days and rupees, is the heavy-base full-life post; reorder points and safety stock follow the hub's production formula.

What to buy, and what to skip

Five items, chosen on page statements, price and stock on 1 October 2026. CSI publishes no wick-performance data, so nothing is ranked on burn results. Oil candle counts use 12 g per 150 g candle at 8% and 9 g at 6%.

Skip for this test: Steel Wick Holder (₹250.00 for 5): a single-wick 6 cm pool doesn't need a three-hole bar; the Wick Centering Device (₹118.00 for 5) is the cheaper way to centre. Performance Wooden Wicks (₹590.00 for 10): a wooden wick would change the wick and the glass reading at once. A non-contact thermometer: CSI doesn't list one; the Pen Thermometer (₹354.00) is for wax, not glass.

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