This is a nickel-free tin-cobalt alloy bath for decorative finishing, and it is the version to look at when a dark gun-color finish has to be produced without nickel. The colour comes from the tin-cobalt deposit itself, laid over a fully bright underlayer, and it reads as the deep black pearl tone that decorative buyers specify on visible parts. Three components make up the system — a bath initiator, a replenishing agent and a brightener — dosed into a potassium pyrophosphate electrolyte. Because the three are replenished separately, the operator can correct colour and brightness without tipping the rest of the bath out of balance.
Rack and barrel work both run on the same chemistry, which matters in a metal plating process handling mixed orders: small parts go through the barrel, larger or flat decorative pieces go on the rack, and the deposit behaves the same way on both. Typical work is consumer-facing hardware — eyewear, bag and belt fittings, jewellery findings, lighting trim, buttons and small die-cast housings — where the finish is seen at arm's length and the specification rules nickel out.
Day to day this is an alkaline bath run at moderate temperature with the cathode moving. It is a complete make-up rather than an additive for an existing nickel-based dark bath, and the parts going into it need a bright underlayer for the black pearl tone to sit properly. If your line already runs tin plating or another alloy finish, the working discipline will feel familiar, since coating production chemicals built on a dissolved base follow much the same order: dissolve the base, add the components in order, confirm pH, electrolyse the bath, then start production.
| Parameter | Value |
|---|---|
| Potassium pyrophosphate | 150~200g/L |
| Bath initiator | 50~60 ml/L |
| Replenishing agent | 14~20 g/L |
| Brightener | 30~40 ml/L |
| pH | 8.5~9.5 |
| Temperature | 35~45 °C |
| Anode | Tin plate |
| Cathode current density (Dk) | 0.2~1 A/dm² |
| Cathode movement | Required |
| Deposit appearance | Gun-color / black pearl over a bright underlayer |
| Line type | Rack plating and barrel plating |
Replenish on ampere-hours. As a general guide the bath takes 500~1000 ml of initiator, 2~3 kg of replenishing agent and 1000~1500 ml of brightener per KAH, adjusted to the workload actually going through it. Most metal plating process lines already log ampere-hours for other baths, and this one benefits from the same discipline: the three components do different jobs, so one cannot cover for another when a figure falls short.
Keep the base salt consistent. Potassium pyrophosphate quality affects the bath at make-up and every time material is added. Staying with one grade from one source removes a variable that is very hard to trace later.
The underlayer must be fully bright. A dull or hazy underlayer shows straight through the black pearl tone. If parts come out patchy, inspect the layer underneath before changing anything in this bath.
pH correction. Adjust with acetic acid or potassium hydroxide, and take the reading before the shift rather than after a reject.
Keep a colour panel. Retain a plated panel from an approved run and compare new parts against it. A drift in tone shows up on the panel long before it shows up in a customer complaint.
The colour in this finish is produced by a tin-cobalt alloy, not by nickel, so it should be judged against an approved panel rather than against the output of a nickel dark bath. Expect a deep gun-color that reads black pearl in daylight; the tone comes from the alloy and the underlayer together, which is why a change in the underlayer shows up as a change in the finish. The chemistry belongs to the tin plating family rather than the nickel family, and that is the simplest way to explain it to a customer who asks what replaced the nickel.
It is a different set of plating chemicals from a nickel-based dark bath, so plan a fresh make-up rather than a top-up. The tank, the rectifier and the movement on the cathode carry over; the anode becomes tin plate and the bath runs alkaline at moderate temperature. Confirm that tank lining, coils and barrels suit those conditions before the first make-up, and look at the plating process around the bath — cleaning, activation and rinses — because the black pearl tone will not cover for a weak underlayer.
If the switch is being made for a specific customer, the practical test is a rack of their standard parts run against the finish they already approve: same underlayer, same part, side by side in daylight. Share the results with us and we will read them with you; confirm colour tolerance, coating thickness and the corrosion expectation for the end use before a production lot is committed.
Fengfan has worked in surface finishing since 1984 — more than 40 years — and the plating chemicals catalogue covers alkaline systems, alloy formulations and auxiliary additives for both decorative and functional coatings, including nickel-free alternatives such as this one. Research, chemical synthesis and quality testing sit inside the same operation, which is what allows a formulation to be held steady from one production batch to the next instead of drifting with a change of source.
That background matters most when a bath is being set up for the first time. Whether the underlayer you already run will carry the tone, how the replenishment figures should be read against your workload, what the deposit should look like on a part with deep recesses — these are answered by people who work with these systems daily, and the same contact stays with the case after the goods are delivered.
Choosing the right match is where most sourcing decisions stall. As a trading supplier, we keep one point of contact from first enquiry to after-sales: tell us what you are making and the conditions you work under, and we shortlist the closest matches from our supplier network, compare specifications and arrange samples before you commit to a bulk order. If something does not behave as expected, we work with the supplying partner on the cause and a practical fix, and stay with the case until it is settled. Email, WeChat or WhatsApp enquiries get a reply within 24 hours.
The obvious one is that no nickel enters the bath, so a dark decorative finish can be quoted on parts whose specification or end market rules nickel out. Beyond that, the deposit is hard and wear-resistant, the tone holds evenly across a rack or barrel load, and the three components are replenished separately so colour can be corrected without rebuilding the balance. The trade-off to plan for is appearance matching: judge the result against an approved panel rather than against a nickel bath, because the colour comes from a different alloy and will not be an exact visual copy in every light.
In most cases yes. It runs on standard equipment — a tank suited to an alkaline bath, a rectifier, a tin plate anode and cathode movement — so the main work is a clean make-up and a check that tank lining, coils and barrels suit the operating band. What cannot be done is topping up a nickel-based dark bath with it; this is a separate bath. Send us your line details and the parts you intend to run, and we will tell you what has to change before the plating process is switched over.
Run the bath at 35–45 °C and pH 8.5–9.5 with a tin plate anode, and keep the cathode moving throughout — the deposit does not come out even without it. Current density sits at 0.2–1 A/dm²; barrel loads of small parts generally work at the lower end of that band, while racked work with larger flat faces can use the upper end. Steady temperature matters more than an exact figure inside the band, because a bath that swings hot and cold changes tone before it changes anything else.
Where a part calls for it, we discuss process adjustments with your engineers rather than simply supplying a drum: the substrate, the underlayer, the finish target and the way parts are jigged all affect the result. Tell us what you are plating and what the customer has approved, and we will say whether this salt is the right starting point or whether another system in the plating chemicals range fits better. Support continues after delivery, and bath questions go to the same contact.
A fully bright one. The black pearl tone is thin and follows the surface beneath it, so haze, dullness or a polishing scratch in the underlayer reads as a variation in colour once the part is finished. In practice that means the layer below has to pass as a finish in its own right before the parts ever reach this bath.
Yes — the same make-up serves both, which is one of the reasons the system suits mixed-order shops. What changes is current density and how the parts are presented: barrel loads rely on good tumbling and sound contact, racked work relies on jigging that keeps the visible faces facing the anode. Running both from one bath also leaves you with one set of replenishment figures to track instead of two.
