I’m Using an 8 cm Jar and the Wick Looks Correct Until the Candle Reaches the Lower Third — Why Does the Flame Become Increasingly Aggressive Near the Bottom?

Why the bottom of an 8 cm jar burns differently from the top

At the first burn the flame sits near the rim of a full jar. It is surrounded by cool glass, over a deep block of solid wax that soaks up heat and a short wall that lets warm air out. By the lower third the flame sits a few centimetres from the base, inside a glass tube that has been heated over many hours, over a thin layer of wax that is nearly all liquid by the end of a session. The same wick in a different place does different work.

This is the late-burn pattern the diagnostics series describes: the flame gets larger as the wax level falls and a pool that becomes extremely deep near the bottom. Those posts own the trimmed-versus-untrimmed twin and the depth chart; this page doesn't repeat them. What it adds for an 8 cm jar is one question those tests don't settle: how much of the aggression is heat you stored by the way you burned? That matters because the answer decides what you change. Stored heat is fixed by a care instruction that costs nothing. A wick too big for the bottom needs a smaller wick, and in CSI's range that is a full rung that can cost you the top of the candle.

Three things that build up as the wax level falls

We read "8 cm" as the outside with a 0.35 cm wall, so 7.3 cm inside, and we assume an 8.5 cm jar with a 0.6 cm base. Both are our assumptions; CSI lists no 8 cm jar, so measure yours (inside at 2–3 heights, as in the external-versus-internal diameter post). Our worked-example fill is 200 g at 8% (16 g of oil + 184 g of wax). By the water-weight rule of thumb (wax at about 0.86–0.9 of water; labelled) that is a column about 5.4 cm tall. With a stop at about 1 cm left (36–38 g), the burnable wax splits into thirds of about 54 g. The upper third ends at about 146 g left and the lower third starts at about 91 g, with the wax about 2.5 cm deep.

Stored heat, the one that depends on you

Depth is read with a marked skewer, as in the within-session depth curve. Of the three, stored heat is the one most affected by how the candle is burned. Glass and wax both hold heat after the flame goes out, and they give it up over hours, not minutes. Light a lower-third session an hour after the last one and the flame starts in a jar that is still warm. The pool reaches its full depth sooner, and the trimmed flame commonly runs taller. Light it the next evening and it starts from room temperature. Customers do both: once an evening, or a long Sunday of relights. So the test has to cover both.

The exposed wick, and the tab

Trim the wick before every session and the exposed length resets, but only at the start of the session. During a hot lower-third session the pool can drop quickly, and the wick left standing above it grows. It is worth reading the wick at 1 hour as well as at lighting. Very near the base there is a separate effect: a flame that suddenly drops or drowns close to the tab is the late-stage drowning post, and it is the opposite of what this page is about.

Stored heat or wick size: what the rest test separates

A candle that turns aggressive in the lower third is compatible with two stories. In the first, the wick is right for this jar at every depth when the jar starts cool, and the problem is heat carried over from a recent session. In the second, the wick puts out more heat than the bottom of this jar can take, however long it rests. You can't tell the two apart from a single candle burned on whatever schedule suited you. You can if you hold the wick constant and vary only the rest.

This is not the same as the 7 cm bottom-zone shortcut, which pours shallow candles to screen the lower zone faster. The rest test runs on full candles, because stored heat is a property of the whole burn history, and a shortcut candle doesn't have one.

The rest-interval test, session by session

In pattern 1 the overnight arm stays inside the practical flame range and near the depth target to the stop, while the short-rest arm climbs further every session. That is heat carried over, not the wick. In pattern 2 (in the diagram) both arms run over 5 cm from the first lower-third session and the gap between them is only 0.6 cm. That wick is too much for the bottom of this jar, whatever the customer does.

Reading the two arms

The first row is the good news, and it is common enough to test for before you touch the wick. What the label should say, and how far to trust customers to follow it, is the label-policy post. If you keep the wick on a stored-heat verdict, your session limit should come from the overnight arm's behaviour, not from how the short-rest arm failed.

The second row is where CSI's short range bites. One rung down from C2 is C1, and C1 may not reach the glass at the top of an 8 cm jar. That is the mirror image of the one-rung-up post, where the bigger wick fixes the top and risks the bottom. If C1 tunnels at the top and C2 runs hot at the bottom, your answer sits between two rungs where CSI lists no sized wick. Say so in your log and ask us. We would rather tell you than sell you the wrong wick. If the jar narrows at the base, that is part of it too: the post on a jar that gets very hot during the final burn covers the jar side.

What the test costs

That is ₹163.22 a candle before the jar. From nothing, the cash outlay is ₹1,378.40 with the Wick Setting Tool, or ₹1,097.40 with a pack of five centering devices instead. Costs are worked examples and exclude jars, labour, freight, packaging and GST. The time is the real cost. The upper two-thirds are burned on one schedule for all four, and the short-rest arm then finishes sooner than the overnight arm, so plan the calendar around the overnight pair. If pattern 2 sends you to C1, the next pair adds a ₹118.00 C1 20-pack and a full life of its own.

What to buy, and what to skip

Four items, in the order the test uses them, chosen on page statements, price and stock on 29 September 2026. CSI publishes no wick-performance data, so nothing here is ranked on burn results. Oil counts are at 16 g (a 200 g fill) and 12 g (a 150 g candle).

Frequently asked questions