Rate, weight and purity
The metal rate changes daily and the bill is built from it, so the rate has to be updated once each morning and applied to every sale afterwards rather than remembered. Purity — 22K, 18K, 916 — belongs on the item because it determines the rate and because it is what the customer and any later valuation will check.
Making charges and wastage in the open
Making charge and wastage are where jewellery bills are disputed, almost always because they were folded into a single figure. Shown as their own lines against a stated weight, the customer can see how the total was reached and the conversation ends. It also means your own margin on labour is visible rather than mixed into the metal.
Old gold exchange
A large share of sales involve old ornaments taken in part payment, which means a weight, a purity assessment and a deduction recorded against the same bill. Doing that on the invoice rather than on a slip is what makes the final amount explicable — and it gives you a record of what came in, which matters for your own stock and for any later question.
HUID, hallmarking and the invoice
Hallmarking requirements mean the invoice increasingly has to carry identifying detail, and reconstructing it later is not possible. Keeping purity and hallmark or HUID detail on the item and the bill costs nothing at the time and is exactly what a customer, a valuer or an inspection will ask for. Confirm the current requirements with your CA or association, because they have changed more than once.