My Replacement Wick Has the Same Length and Apparent Thickness as My Old Wick — Why Might It Still Burn Differently?

Seven properties, and a ruler checks two

A wick is a small fuel pump. Melted wax and fragrance climb the braid by capillary action, reach the flame and burn. How fast that happens decides the size of the flame, the heat it delivers to the wax, how wide and deep the pool becomes, how hot the glass gets and how quickly the candle is used up. Length only decides how far the pump reaches; apparent thickness is a rough guide to how much it can carry. The rest of the story is in the construction: how tightly the yarn is braided, how many plies it has, what fibre it is, whether it is primed with wax and how much, whether there is a core, and how the tab and neck are made.

Two wicks can match on length and on a quick look at thickness and still differ on every one of those. It is common for a looser braid to carry fuel differently from a tighter one of similar outside width, for a primed wick to stand and light differently from an unprimed one, and for a cored wick to behave differently deep in the pool. None of that is visible across a shop counter or in a product photograph. Here is what each property can change and whether you can check it before burning.

The right-hand column is the useful one. Four of the seven can be partly checked with a scale, a magnifier, a blade and a ruler in about fifteen minutes. That will not tell you the wick burns the same, but it can tell you that it is different, and which burn lines to watch hardest. Two properties — fibre and treatment — can only come from the supplier's description. One — curl — only shows when it burns. This is also why CSI does not describe any of its wicks as equivalent to another brand's size: the construction details that would support such a claim are not published for Eco Candle Wicks, Cotton Braided Wicks Ready Made or Performance Wooden Wicks.

Bench checks before you light anything

Bench checks are cheap and fast, and they are not a substitute for a burn. Treat them as a way to decide where to look in the burn test, not whether to run it. If every bench check matches, you still burn. If a bench check differs, you already know which scoring lines matter most.

What stays valid and what you retest

Your wax, oil, load and jar are unchanged, so the results that describe the unlit candle carry over. Everything to do with the flame does not. The matrix below uses the series' four labels: KEEP (still valid), CONFIRM (short side-by-side check), REPEAT (full retest) and NEW (a test you never needed before). There is no NEW line here because the wick type — cotton — is unchanged; if you are moving to wood, go to the cotton-to-wooden post.

The two CONFIRM lines deserve a word. Wick seating and early ignition are where a priming or stiffness difference shows first, and they are checked on every candle as part of the pour and the first burn — no extra candles needed. If either looks different, carry that note into the REPEAT lines: a wick that leans after pouring will give an off-centre pool and uneven glass heat, and you want to know whether that is the wick or the way it was set. The wick-change hub explains the bracket approach if you are choosing between two new wicks rather than confirming one.

The six-candle side-by-side test

Melt one batch of wax and oil and pour all six candles from it. In Luxury Soy Wax CSI 464, CSI's own guidance for melting and pouring is 80–90°C — confirm it on the product page, and use whatever your approved recipe already specifies. At 8% each 200 g candle takes 16 g of oil and 184 g of wax; CSI 464 is rated by the wax maker up to 10% fragrance load, so 8% (16 g of the 20 g maximum per candle) sits inside it. Set the old wicks and new wicks with the same method — same stickers, same centring device — and cure all six together to the checkpoint your recipe already uses.

Burn in cycles of about 3–4 hours with a full cool-down between them (a commonly used cycle; a working practice). Trim every wick to the same length before every burn, because a new wick that arrives with a different length above the tab will otherwise be tested at a different trim. Keep going through at least three burns for the screen, then carry both groups to the end of usable wax. Curl and consumption rate often need a few burns to show a consistent pattern, and end-of-life is a REPEAT line in its own right.

Scoring sheet with a bench column

This sheet adds one column the generic sheet in the hub does not have: which construction property each line is most sensitive to. When a line differs, that column tells you which bench check to go back to, and what to ask the new supplier.

CSI publishes no numeric limit for flame height or jar temperature, and this sheet does not invent one. The safety rule is: no worse than your approved control on every safety line — flame, soot, mushrooming, glass heat, end-of-life — and within your jar supplier's guidance and the candle fire-safety standard you work to (ASTM F2417 is a commonly cited US standard; use its methods if you follow it). A hotter flame is never accepted in exchange for a stronger scent.

Deciding: same, different-but-acceptable, or not this wick

The middle verdict is where most honest wick swaps land. Two wicks that look alike often turn out to be close but not identical. That is fine, as long as the difference is on the right side of every safety line and you would sell the new candle without apology. What matters is that you decide it deliberately, from a sheet, and write down why — not that you discover it from a customer review. If you find yourself adjusting the fragrance load or the fill to make the new wick work, stop: that is a formulation change, and the 5,000-wicks post explains when it is and is not the right move.

The priced six-candle kit

The kit prices the six-candle test in Luxury Soy Wax CSI 464 with British Rose Fragrance Oil at 8%, 200 g candles and a 5% pour-loss allowance (a labelled working assumption). If your production candle uses different wax or oil, use yours: the only thing that should change between control and test is the wick. The ten Cotton Braided wicks cover three test candles, one or two spoiled sets, and five or six wicks for the bench checks.

Spread over an example production run of 300 candles — replace it with your own — the kit adds ₹6.77 per candle. Labour, electricity and your time are not included; add them from your own figures if you cost tests that way. The British Rose here is bought as 100 g + 15 g (₹436.60) rather than two 50 g bottles (₹519.20 for 115 g), because on British Rose the 100 g bottle is genuinely cheaper per gram (₹3.42) than the 50 g (₹4.25) — one of the oils where the small-pack premium is real.

Recording the wick so this never happens blind again

Whatever the verdict, the bench line you wrote in step six is the start of a proper wick specification. If the new wick passes, it replaces the old line on the recipe card. If it fails, you now know exactly how it differed, which makes the next conversation with a supplier far more useful than "it burns differently". Here are the fields worth keeping for every approved wick.

Keep ten wicks from each approved order in a labelled bag. The next time a pack arrives, run the ten-wick weigh and the scratch test against the retained bag before you use it. That takes two minutes and catches the most common silent change — a different wick sent under the same description. The reproducibility post shows how to record the whole candle this way, and the storage-testing post explains why a wick-only change rarely needs new storage tests.

Questions to ask the new supplier

A good supplier will not mind these questions, and the answers make your bench checks faster. Ask what the wick is made of (fibre and any core), whether it is primed and with what kind of wax, the braid type, the neck height above the tab, and whether the construction has changed recently. Ask for their size recommendation for your jar diameter, and treat it as a starting candidate, not a result. For CSI's own wicks, the honest answer to several of these is that the details are not published — we can tell you what is on the product page and help you plan a test on WhatsApp, but we will not give you a construction figure we do not have.

Whatever the answers, the test still runs. The questions change the order in which you look at the scoring lines; they do not remove any. If you are under time pressure because an order is due, the emergency 1,000-candle wick post sets out the smallest defensible test, and the full retest checklist lists every line in one place.

Frequently asked questions