Silver-Graphite Brushes & Slip Rings
Weigh it against its size — a silver-graphite brush is startlingly heavy (ρ 4–7 vs ~1.7 g/cm³ for carbon) and leaves a bright metallic grey streak on paper; if it feels like a lump of charcoal, it is a lump of charcoal.
How to spot it
Rectangular block 5–40 mm with a braided copper pigtail and terminal lug, often in a spring-loaded holder, grey-silver on a fresh cut rather than matte black. Grade codes stamped on the side: Mersen MC79P/MC78/CG957/MC837 (≥80% metal), CG677 (55–80%), plus Helwig, Morgan and Schunk equivalents. Found on wind turbine slip rings, wound-rotor motors, aircraft starter-generators, alternator exciters and synchros — not in drills, vacuums or car starters.
Metal content
| Metal | Quantity | Notes |
|---|---|---|
| Silver | 40–95% by weight, typically 70–90% | Slip-ring/wind-turbine grades; at 80% that is 363 g Ag per lb |
| Copper | pigtail + commutator segments | Cut the pigtail off or it dilutes your assay 15–30% |
| Base metal | electrographite, 0% metal | Most brushes you will ever see are this |
At 4 Aug 2026 spot prices that works out to $690 per pound of contained metal — Silver 363 g = $690. A refiner paying $615 returns about 89% of that, which is normal: refining costs money and the buyer takes a margin.
Safe removal
Working temperature: No heat — mechanical removal only
Lift the brush holder spring and slide the brush out. Cut the copper pigtail flush — the pigtail must come off before assay or you dilute the lot. Slip rings unbolt; a thinly silver-plated ring is generally not worth stripping, sell it as bronze.
Hazards
NEVER dry-cut boards indoors without extraction.
NEVER short a large capacitor with a screwdriver. It welds the tip, blasts molten metal at your face, and can rupture the can.
NEVER dry sweep or use compressed air on a scrapping bench. HEPA-vac or wet-wipe only.
NEVER grind, burn, torch or braze cadmium-plated or AgCdO material, and don't inhale the black contact dust.
Before you scrap it
The common trap
Questions
How much gold is in silver-graphite brushes & slip rings?
Silver: 40–95% by weight, typically 70–90%. Copper: pigtail + commutator segments. At current spot that is about $690 of contained metal per pound.
How do you identify silver-graphite brushes & slip rings?
Weigh it against its size — a silver-graphite brush is startlingly heavy (ρ 4–7 vs ~1.7 g/cm³ for carbon) and leaves a bright metallic grey streak on paper; if it feels like a lump of charcoal, it is a lump of charcoal.
How do you remove silver-graphite brushes & slip rings safely?
Lift the brush holder spring and slide the brush out. Cut the copper pigtail flush — the pigtail must come off before assay or you dilute the lot. Slip rings unbolt; a thinly silver-plated ring is generally not worth stripping, sell it as bronze.
Is silver-graphite brushes & slip rings worth more working than as scrap?
Mixed. New/NOS silver-graphite sets for wind turbines or aircraft generators sell $30–150/set, often more than the silver because they are spares-market critical. Worn brushes have no resale — if more than 50% of original length remains and the grade is legible sell as a part, otherwise refine.
Related in Contacts & relays
Get this offline → The full guide runs in your browser with no signal, and you can add your own photos.