Sodium Sulfide

Product Overview

Sodium Sulfide (Na2S) is the workhorse sulfide donor of the finishing shop - a yellow to reddish-brown flake that hydrolyzes in water to a strongly alkaline solution rich in free S2- ions. In metal finishing it does three distinct jobs: it colors copper and brass into antique brown-black sulfide finishes (the raw chemical behind many proprietary antiquing concentrates), it purifies plating solutions by precipitating heavy metals, and it removes dissolved heavy metals from effluent as extremely insoluble sulfides. In QLQ's finishing plants it supports antique hardware lines for zipper sliders and belt buckles and keeps zinc and nickel process solutions free of copper and lead. Two commercial families are common: standard reddish technical flakes (Na2S ≥ 60%) and low-iron yellow flakes (Fe ≤ 0.005%) which are preferred when a clean, reproducible sulfide color is required - iron in the grade tints the sulfide film and shifts shade. Grades sold for paper pulping or mining flotation are not held to the impurity limits plating and effluent work need, so ask for the low-iron classification by name.

Product Identity (Encyclopaedia Card)

What it is and what it does. Sodium sulfide is the classic blackening and antiquing agent for brass, bronze and copper alloys, and it is also used as a component of some colouring and etching solutions.

• Yellow to red-brown flakes; it reacts with copper and silver ions to give the black sulfide film used in antiquing.
• Also used in the colouring of brass hardware and in the treatment of steel before some phosphate processes.
• Strongly alkaline and it releases hydrogen sulfide if acidified - never acidify a sulfide bath.

Typical Use in a Plating / Finishing Line

Safety, Handling & Storage

Quality Documents Shipped With Every Batch

Buyer Questions We Answer Every Week

Where It Is Used in a Finishing Plant

Sulfide coloring is an immersion conversion reaction: S2- reacts with the copper or brass surface to grow a compact cupric-sulfide film whose shade runs from light chocolate to near-black as concentration, temperature or time increases. Because the film follows every contour, recessed detail darkens first and raised surfaces can be highlighted afterward - the classic antique relief look. The same sulfide chemistry does useful purification work: in alkaline and cyanide process solutions, a small test dose of sodium sulfide throws out copper, lead and cadmium as sulfide sludges that are then filtered, leaving the working metal untouched.

One warning carries over between all three uses: sulfide must never meet acid. Acidifying a sulfide solution liberates hydrogen sulfide gas instantly, so sulfide coloring tanks, purification additions and sulfide sludge lines are kept physically separate from acid dips and pickles.

How to Check Quality Before Loading a Batch

How QLQ controls it: sulfide deliveries are quarantined until the assay and iron figure on the COA match the purchase order, and a small brass test panel is colored with the actual lot before any of it is released to the antiquing line. The lot number follows the drum into the tank record, so a shade complaint can be traced to a single delivery within a day. Only lots that pass all five checks above are accepted.

Common Problems & Fixes (Workshop Table)

Handling & Safety for the Plating Line

• Alkali burn risk: dissolved sulfide is a strong caustic (pH > 12). Wear splash goggles, neoprene or nitrile gloves and a rubber apron when opening bags, dissolving flakes or handling solutions.
• Hydrogen sulfide (H2S): contact with any acid - even acid drag-in on parts - liberates toxic H2S. Ventilate the sulfide area separately, never position acid dips upwind of it, and treat smell fatigue as a warning that exposure is already dangerous.
• Dissolving: add flakes to water with slow stirring and let the heat of solution dissipate; do not add to hot acid or hot water where boiling can spray caustic solution.
• Storage: keep bags sealed on dry pallets, away from acids, oxidizers and moisture. Damp or CO2-exposed sulfide develops a carbonate crust and loses assay.
• Spills and waste: do not wash sulfide into acid drains - that generates H2S in the sewer. Collect sulfide-bearing solutions and treat with iron salt or oxidize residual sulfide before discharge to meet local sulfide and metal limits.
• First aid: eye splash - flush 15 minutes with water and seek medical attention; skin - remove contaminated clothing and wash thoroughly; report all H2S exposures.

What It Does on Iron, Zinc Alloy, Copper and Stainless Steel Parts

FAQ

Setting up an antique line or a bath purification program? QLQ supplies low-iron sodium sulfide with COA and helps customers in 10+ countries size doses, build sulfide-safe tank layouts and train operators. Contact us with your bath analysis.