A Customer Complaint Appeared Three Months After Production — How Can Retained Raw-Material Samples Help Determine Whether the Supplier Batch Contributed?

Two kinds of retain answer two different questions

When a complaint lands three months after production, you need to separate three possible causes: the raw-material lot, your own process on that production day, and what happened after the candle left you. Retained samples are how you pull those apart, but only if you understand what each kind can prove.

A finished-candle retain is one or more candles from the production batch, kept back and stored. Burning it shows whether the fault was built into the batch when it left you. It cannot tell you whether the wax, the oil, the wick or your pouring caused it, because all of those are already locked inside the same candle.

A raw-material retain is the small bag of wax, bottle of oil and packet of wicks you set aside from each lot at goods-in. Remaking a test candle from those retains, beside one made from your current approved lots, isolates the material. If the fault follows the old lot, the lot contributed. If it appears in both, look at your process or the design. If it appears in neither, look at how the candle was stored, shipped or burnt.

Read the table as a guide, not a verdict. Burn tests vary, and one candle per condition is thin. Where results are borderline, repeat the condition that matters before drawing a conclusion.

Worked case: a smoky Woody Oud candle from June

A customer writes in September. Their 200 g Woody Oud jar candle, bought in July, smoked and left black marks on the glass after a few burns. Your batch code on the base leads to a June batch sheet that records: CSI 464 wax from one invoice, a 1 kg bottle of Woody Oud received in May, thin Eco wicks from a 500-piece packet, 8% fragrance load, pour and add temperatures, and a 72-hour cure before dispatch. At 8% of a 200 g candle, each jar held 184 g of wax and 16 g of oil.

You kept one finished candle from that batch, plus the standard raw-material retains: about 100 g of that wax lot, about 15 g of that oil lot and five wicks from that packet. Here is how to use them.

Why the small vessel still works

A votive is not the customer's candle, and a wick sized for a 200 g jar may not suit it. That is acceptable because the question here is relative: does the old lot behave differently from the current lot under identical conditions? Choose a wick that burns cleanly in the votive with current materials, then hold it constant. If you need to reproduce the customer's exact candle, you need a full 200 g jar, which is one reason some makers retain 200 g of wax rather than 100 g.

Deciding how far the problem reaches

The same batch sheet tells you how many candles share the suspect lots. If the June batch used 25 kg of that wax lot at 8% for 200 g jars, it produced 25,000 ÷ 184 = 135 candles, rounded down. One complaint out of 135 does not prove a batch problem, but it does tell you how many customers could be affected if the retain tests confirm one.

Taking a confirmed lot issue to the supplier

If the retained-lot remake reproduces the fault and the current-lot remake does not, you have something worth sending: the batch sheet line with the lot or invoice number, the date received, photos of both test candles mid-burn, and your session-by-session notes. That is a factual conversation rather than a complaint.

For materials bought from CSI, send it on WhatsApp to +91 7397976926 with the invoice reference. We do not publish lot numbers on product pages, which is exactly why your own receipt record matters: the invoice number and date received are the link back to what was sent. If a CSI lot is the one that reproduces the fault, we would rather see your evidence than have you quietly change your formula around it.

The honest reverse also applies. If your retains show the old lot was fine and the design is marginal, the fix is yours, and no supplier change will cure it.

What this complaint should change in your retention habits

Three months is a common delay between production and a complaint, because candles sit in shops and cupboards before they are burnt. If you found yourself without a finished-candle retain, or with a wax retain too small to pour a full-size comparison, adjust now. Keeping one or two finished candles per production batch, stored with the raw-material retains, is a reasonable starting point to validate. Record the burn result of every investigation in the retain log so the next complaint starts with history rather than a blank page.

Finally, keep the retains from any lot that an investigation implicated for longer than your normal disposal rule. If a later delivery shows the same behaviour, you will want both on the bench together.

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