Compound for Silver: The Four Jobs a Steel Compound Cannot Do

A compound for silver is not a milder steel compound. Silver fails in ways steel does not: it tarnishes chemically rather than corroding electrochemically, it is soft enough that the compound's aggressiveness is a money decision, and its most common alloy — sterling, 925 parts silver to 75 copper — has a second phase that chemistry can attack before the silver goes. A compound carried over from a stainless job will usually still produce something that looks bright for a day. What it will not do is leave a surface that survives the week, or hold the detail the part was made for.

This page is the set of judgements that decides which compound a silver part needs, how to tell a compound problem from a media or rinse problem, and what to test before you accept a recommendation. Where numbers appear they are a starting band: a published cycle assumes a material and a removal that may not be yours, and silver is exactly where that sentence bites.

What you see when a steel compound has been run on silver

Four symptoms come back from the same cause, and they are usually reported as four different problems:

What you see	What it usually is	Where to look first
Bright out of the machine, black again in two to five days, starting in recesses and along seams	Compound residue left in crevices, holding sulfur and moisture against the surface	Rinse and dry discipline, then compound rinsability
A pink or copper cast on sterling, worst on high spots and near solder joints	The copper-rich phase attacked or preferentially exposed	Compound chemistry and pH, not the media
Detail rounded off — engraving softened, milled edges lost	Cut too aggressive for the section thickness	Compound function class and cycle length
Grey bloom after drying, no tarnish pattern to it	Water-borne residue dried in place: a rinse problem wearing a compound problem's clothes	Final rinse water and drying, not the drum

The first row costs the most, because the parts passed inspection. A part that tarnishes on the shelf is not a fault the machine reveals — it shows up in the customer's display case, and by then the batch is packed.

Why silver is a different chemical case, not a softer steel case

Tarnish is a film, not a corrosion product. Silver darkens when it meets sulfur-bearing gases and forms silver sulfide. The film is nanometres thin at first and cleaning does not remove it — it is removed by cutting it away or converting it back. That changes the compound's job: on steel it manages an electrochemical environment; on silver it manages a film-removal step that must stop before it takes silver with it.

The alloy is where the trouble hides. Sterling is 92.5 % silver and 7.5 % copper, and the copper does not sit still. It can be attacked preferentially by chemistries that leave pure silver alone, producing the pink cast jewellers call by a dozen local names. Fine silver and sterling are two different process specifications, and a compound approved on one is not approved on the other.

Firestain is not a compound problem and never will be. Where a sterling part has been annealed or soldered, copper oxide can form below the surface. Polishing cuts through the fine silver skin and exposes it as a dark or purplish cloud that returns as fast as you polish it. No compound removes it, because it is not on the surface; recognising it early changes the process upstream, not the drum.

Chloride and residue finish the job. Tap water carries chloride, which leaves its own marks on silver, and residue in a crevice holds both chloride and sulfur against the metal. That failure is designed in during rinsing, which is why the last section is about the parts of the process that are not the compound.

The four jobs a silver compound has to do

Sort any product against these four, in this order. One that is good at one and silent about the others is half a spec.

1. Lift the sulfide film without cutting the silver under it. This is the balance point. A cutting compound removes tarnish and a measurable amount of silver with it; a burnishing compound removes the film with far less stock removal. For a thin section, a hinge leaf or an engraved face, burnishing is correct and cutting is a rework order. Ask which of cut, burnish, clean or protect the product is, and what it is not for.

2. Hold a shallow, uniform cut so detail survives. Silver work is judged on crispness — an engraved border, a milled step, a setting seat. Uniformity preserves it; a fast uneven cut rounds one edge and leaves the other. That means fine media and a compound that keeps the cut from loading, and the sizing rule for every loose-media process applies unchanged: media no larger than about one third of the smallest feature. Ceramic bodies run from about 3 mm to 10 mm, plastic from about 10 mm to 25 mm, and the fine end of the ceramic range is where most silver cut work sits.

3. Leave nothing behind that can feed a re-tarnish. Residue is not cosmetic on silver; it is a delayed failure. A compound that rinses clean in two changes of water beats one that brightens half a shade better and leaves a film in every recess — the specification line most often missing from a quotation.

4. Where a protection function is claimed, be precise about what it is. A tarnish inhibitor buys hours to days between finishing and packing, and does not survive handling, wrapping or a humid store. It is not a lacquer and not a substitute for dry packaging.

A polished medical plate, the surface standard a silver compound is judged against.

The failure table, with the adjustment attached

The four-column version, because "check the compound" is not an instruction anyone can act on:

Symptom	Likely cause	What to check	What to change
Tarnish returns within days, in recesses first	Residue holding sulfur and moisture	Rinse stages, water quality, drying completeness	Add a clean-water rinse, dry immediately, check blind features
Pink cast on sterling, high spots worst	Chemistry attacking the copper phase	Compound pH, and whether it was specified for sterling	Change the compound, not the dose
Engraving and edges softened	Cut too aggressive for the section	Media size against the feature, cycle length, compound class	Finer media, burnishing compound, shorter cycle
Grey bloom with no tarnish pattern	Dried-on water residue	Final rinse, water hardness, dryer temperature	Cleaner final rinse, faster dry, less carry-over
Bright but blotchy across a batch	Dose or flow drifting between cycles	Dose method (volume or weight), logged per cycle	Fix the dose method before changing products
Parts float and the cut stalls	Over-foaming lifting the load	Foam level at mid-cycle	Lower-foam compound, or reduce the dose

Two entries deserve a sentence each. The pink cast survives every downstream step: it can be plated over, it cannot be polished out, and it is created by chemistry rather than media, so re-running the same charge fixes nothing. The grey bloom is the most misdiagnosed: it looks like a compound failure, it is a rinse failure, and a shop that changes the compound first spends money and keeps it.

How to specify a silver part so the compound can be chosen

A silver job quoted from a photograph is a guess. What makes it answerable:

The alloy, by name — fine silver, sterling, a specific sterling variant, or plated. Sterling and fine silver are separate specifications, and plated parts have a rule of their own below.
The mass and the thinnest section, in grams and millimetres — what turns "metal loss" from a worry into a number.
The features that must not change — engraving depth, setting seats, hinge leaf thickness, an edge that must stay crisp.
The finish target in two parts: colour and clarity, plus a roughness figure if the customer measures one. On decorative silver the visual judgement is the acceptance criterion, written down including the lighting it is judged under.
What happens after — lacquering, plating, setting, packing or storage. A part sealed in a bag in a humid warehouse needs a different rinse discipline from one going straight to setting.

The trial has to measure two things, not one: the finish, judged as above, and the metal loss, by weighing the batch before and after — a kitchen scale if the batch is large enough to move it, a jeweller's balance if not. Metal loss per cycle is what decides whether a compound is acceptable on a precious-metal part, and it is almost never quoted. Our standing route: send representative parts including the worst case with the material and the target, and get them back with the cycle time and the consumption measured. On silver, add the weight before and after, and ask for it in writing.

A cheap second test closes the loop the machine cannot: seal a finished part in a container with a piece of sulfur-bearing material for a day. Where the tarnish appears — recesses first, or evenly — tells you whether the problem is residue or the surface.

A mirror surface that reads a hand and a window: the colour-and-clarity target for precious metal.

Where a compound will not fix the part

Compound is one lever, and on silver it is often not the one that is failing:

Firestain. Sub-surface copper oxide, exposed by polishing and returning as fast as it is polished. The fix is upstream — metal preparation and soldering practice — not a product.
A scratch you can feel. Compound refines a surface; it does not level a groove. A fingernail-catching scratch needs a cutting stage first, and on a thin section that belongs on the bench.
Plated silver. The layer is typically a few micrometres, so any compound that removes tarnish by cutting also removes the plate; the failure is a patch of base metal weeks later. Plated work needs the burnishing route or hand work, and a specification that says "do not cut".
Stones, pearls, amber, glued settings, enamel. Loose media reaches everything, including the setting. A compound cannot protect a pearl.
A deliberate patina or oxidised recess. Tumbling removes the contrast by design.
One piece, or five. Setup, charge and rinse dominate; the per-part cost is a bench cost.
A surface that must match a previous batch exactly. Consistency comes from a written recipe — fixed dose, fixed cycle, fixed rinse — not from a brighter compound.

What to ask before you approve a silver compound

Six questions, in the order that saves most money:

"Which function class is this, and what is it not intended to do?" Cut, burnish, clean or protect. A supplier who cannot answer the second half is selling a generic product with a silver label.
"Has it been specified for sterling, or for fine silver?" If the answer is "silver is silver", the pink cast is already in the quotation.
"How does it rinse out, and what does it leave in a blind feature?" Ask about the residue, not the brightness.
"What is the consumption per batch, and is the dose by volume or by weight?" Consumption, not the drum price, is the cost per part. Our compounds ship in 20 kg barrels for the liquid fluids and 50 kg drums for the powders.
"Will you run our worst-case part, and give us the weight before and after?" The trial is the deliverable; metal loss in grams per batch is what makes it a precious-metal decision.
"What is the pack size and the lead time?" Standard configurations ship in 25 to 35 days from the deposit and built-to-order configurations in 45 to 60 days, with media and compound adding about a week. A compound out of stock when the machine lands stops a production start.

Two site facts belong before installation: a powered finishing machine in our range runs on three-phase 380 V or 415 V at 50 Hz, with small models at 220 V, and sits in the 75 to 85 dB(A) at one metre band. Neither changes the compound choice, but both change the room.

FAQ

What is a compound for silver, and is it different from a jewellery compound? It is the working fluid in a wet mass-finishing process applied to silver and its alloys. "Jewellery compound" is a broader trade term covering gold, silver, platinum group and costume work; the silver case carries two constraints the others do not share — the sulfide film and the copper phase in sterling. Treat a generic jewellery compound as a starting point, not a specification.

Can I use a stainless compound on silver? You can, and it will usually look bright on the day. The risks are a cut too aggressive for a thin section, a chemistry not selected with the copper phase in mind, and a residue that re-tarnishes from inside every recess. Those failures appear after the parts have passed — the worst time to find them.

How do I stop silver tarnishing after polishing? Rinse until the water runs clean, dry immediately, keep the parts out of sulfur-bearing packaging, and use a tarnish inhibitor only as a short bridge to packing. A compound supports that chain; it cannot replace it.

Why did my sterling parts come out with a pink tint? The copper in the alloy has been exposed or preferentially attacked. It is chemistry, not a media colour problem, and it does not polish out — plating over it carries it forward. Check the compound against sterling first, then the rinse.

How much silver do I lose per cycle? It depends on the compound class, media, cycle and section, so it has to be measured on your own parts rather than quoted. Weigh the batch before and after a trial and express it in grams per batch and as a percentage of part mass; that number, not a roughness figure, is what a precious-metal process is approved on.

Do you supply a silver-specific compound? We manufacture finishing equipment and the media and compounds that run in it, and the compound range is organised by function and base-metal family rather than one product name per metal. A silver specification is settled the way every other one is: from your alloy, your part and your target, with a trial before it is fixed. We do not publish a silver SKU and would rather say so than send a datasheet that has not been run on your metal.

Max Xu, Sales — Xiamen Jin Tai Jin Grinding Technology Co.,Ltd.

No. 31, Xinchang Road, Xinyang Industrial Zone, Haicang District, Xiamen

info@surface-polish.com

This article describes how a compound for silver is judged and specified; it is not a claim about any specific part's achievable result, and no silver-specific product is offered from a catalogue. A finishing process is set by the alloy, the stock to be removed and the finish required, so the specification for a specific part is confirmed against a trial on that part. We manufacture finishing equipment and the media and compounds that run in it; we do not offer a job-shop finishing service.