Some Jars in My Shipment Have Noticeably Thicker Bases — Could This Affect Heat Distribution Near the End of the Candle?

What a thicker base can and cannot do to your candle

Heavy-bottomed jars are common, and within one shipment some can come out of the mould with noticeably more glass at the bottom than others. You have noticed it because the jars feel different in the hand, or because the inside looks shallower when you look straight down. The question is whether that extra glass changes anything that matters once a candle is poured and burned.

The honest answer is that a thicker base usually has a modest effect on the main part of the burn, where the flame sits well above the floor. Where it can matter is at the two ends of the candle's life: at the pour, because a raised inner floor changes fill height and wick seating, and at the finish, when the flame is close to the glass and the base is absorbing and holding heat.

Measuring base thickness without breaking a jar

You cannot put a caliper through the bottom of a jar, but you can calculate the base thickness from two easy readings. Measure the outer height of the jar from the table to the rim, then use the depth rod of your caliper to measure the internal depth from the rim down to the centre of the inner floor. The difference is the base thickness at the centre.

Then take the internal depth again at three points near the wall, roughly evenly spaced. If those three readings differ from each other by more than a millimetre or so, the floor slopes, and a wick tab placed on it will not stand upright without help. Treat that 1 mm as a suggested starting point to check against how your wick sits in practice.

Worked example: sorting 300 jars with mixed bases

Say your reference jar has an outer height of 80 mm and an internal depth of 73 mm, so the base is about 7 mm at the centre. In a delivery of 300 jars, you measure a suggested starting sample of 30 across all cartons and find 8 with an internal depth of 69 mm, meaning a base of about 11 mm. Treat these as example figures of the kind you would measure yourself.

With an internal diameter of 64 mm, the lost volume is π × 32 × 32 × 4 mm = 3.1416 × 1,024 × 4 = 12,868 mm³, about 12.9 ml less room inside. Fill by weight and the wax surface sets about 4 mm higher in those jars. If your usual headspace is 15 mm, the thick-base jars leave only 11 mm below the rim, which may bring a trimmed wick close to the lid.

Eight out of 30 in the sample is too many to ignore, so it is worth sorting the full 300. Weigh every jar against your reference weight, set aside any that are roughly 25 g or more heavier (a suggested starting threshold for a jar of this size), and confirm a few of those with the depth rod. That turns a vague feeling into two labelled groups.

The end-of-life test that answers the heat question

The only way to learn whether the thicker base changes heat behaviour near the end is to burn candles to the end in both kinds of jar, side by side. You are comparing the two groups, not proving anything about glass in general.

Pre-cut wicks deserve a thought here too. A ready-made wick has a fixed length from the tab, so when the floor rises by 4 mm, the top of the wick rises with it. After trimming, that usually makes no difference, but on a jar with tight lid clearance it can mean the untrimmed wick is bent by the lid in storage. Check a thick-base candle with its lid on before you pack a batch of them.

If both groups behave the same through the final 2 cm, the thick-base jars can be released, with a note of their higher fill line and a check on lid clearance. If the thick-base candles run noticeably hotter, lean, or leave the base uncomfortably warm for much longer, keep them out of production for that product and speak to the supplier.

Recording the result and raising it with the supplier

Write the base readings into the shipment record, along with the count in each group and the decision for each. Keep one jar from each group aside, labelled with the invoice number and date received, as physical references for the next order. If a large share of a shipment has a sloping floor, that is a manufacturing matter to raise, not something to fix with wick stickers and hope.

For CSI jars, send photographs and your readings on WhatsApp (+91 7397976926) and ask whether the glass has changed. CSI does not publish base thickness, jar weight or dimensional tolerances, so treat any answer as information to record rather than a guarantee. Your own measurements and end-of-life results are the evidence that decides whether those jars reach the pouring line.

A last practical point: variation you can see is usually the easiest kind to manage, because you can sort it. The shipments to worry about are the ones nobody looked at closely enough to notice.

Where this page fits

CSI already has guides that cover parts of this question. This page covers the goods-in check for the question above; these go deeper on the rest:

Three things to buy for this job

Frequently asked questions