Keum-boo is one of the oldest ways to put gold onto silver, and one of the most forgiving once you understand it. No solder, no plating tank — just a thin sheet of 24k gold, a warm surface, and steady pressure from a burnisher. Here is how it works at the bench.
Why it has to be fine silver
Keum-boo is a diffusion bond, not a glue and not a plate. When you press 24k gold against clean silver at the right temperature, atoms of gold and silver migrate across the join and lock the two metals together. The bond is permanent and needs no solder.
That migration only happens cleanly against pure silver. Fine silver — 999 — has nothing in the way, so the gold takes almost at once. Sterling is the problem child: its copper content oxidises the moment it meets heat, and that thin skin of copper oxide sits between the gold and the silver like grease on a windscreen. The gold touches the oxide, not the silver, and it lifts. You can still use sterling, but you have to bring a layer of fine silver to the surface first.
Depletion gilding sterling
Depletion gilding — also called raising the fine silver — is the fix. You heat the sterling until the copper at the surface oxidises, then pickle it to dissolve that oxide away. Each cycle strips a little more copper from the top layer and leaves fine silver behind. After four or five rounds the surface turns a soft, chalky white. That frost is your signal: it is nearly pure silver, and it will take gold.
Keep the heat gentle and even, the same control you would use when you anneal and forge silver. You are not trying to melt anything — only to oxidise and remove copper, over and over, until the white holds after pickling. Rinse well and do not touch the face with bare fingers afterwards; skin oil is enough to spoil the bond.
Cutting the foil
Keum-boo uses foil, not gilder's leaf. Leaf is far too thin — it tears if you look at it and carries no body across a join. Keum-boo foil is still thin, a fraction of the thickness of your thinnest sheet, but it holds a cut edge and can be handled with care.
Cut it between two sheets of paper or a folded card so your fingers never touch the gold directly. Small scissors or a sharp craft knife both work. Cut the shapes you want — a moon, a band, a scatter of dots — slightly proud of the finished size, because the edges are where lifting starts and a little overlap gives you room to burnish them down. If you are laying gold over a textured ground, cut generously; foil settles into low relief as you work it. This is a good moment to plan the piece against the ideas in our guide to texturing silver.
The bond — heat and a burnisher
Set the silver on a hotplate, or rest it on a steel mesh and warm it from below with a soft torch flame. You want the surface somewhere around 260–370°C — hot enough to drive the bond, but well below the point where silver anneals fully or solder would flow. A drop of water flicked onto the plate should skitter and vanish rather than sit and boil.
Lay the foil in place with tweezers — a pair of anti-magnetic soldering tweezers keeps your fingers clear of the heat — and press it down with a burnisher. Start from the centre and work outward with firm, overlapping strokes, chasing any trapped air to the edge. Within a few passes you will feel the gold grab and see it settle flat against the silver. A smooth, hard tool matters here: the curved and straight blades in a burnishing tool set let you reach both open ground and tight corners without dragging or tearing the foil. Browse the rest of the tweezers & soldering tools if you need something finer for small work.
When the gold won't stick
Two faults cover almost everything. If the foil simply will not take, the surface is either not hot enough or not clean enough — go back and raise more fine silver, and check your temperature. If the gold tacks but then lifts at an edge or bubbles in the middle, you trapped air or left grease behind. Re-warm the piece and burnish the lifted area again, working from good gold outward; most lifts flatten back down under a little more heat and pressure.
Overheating has its own tell: the gold looks like it is sinking or going patchy, which means it is starting to alloy into the silver and lose its colour. Back the heat off. Keum-boo rewards a steady middle temperature far more than a high one.
Protecting the gold, then darkening the silver
The gold layer is thin, so treat finishing with respect. A hard burnisher will only brighten and consolidate it — run the burnishers over the edges once more to seal them. Keep abrasives away from the gold; a few careless strokes of a polishing stick will cut straight through it. If you need to bring up the silver, do the bright polishing before you oxidise, and by hand — see polishing jewellery by hand for a gentle sequence, and the polishing & finishing range for the right sticks and compounds.
The real reward comes last. Gold shrugs off liver of sulphur, but silver drinks it in, so a patina bath darkens the ground and leaves the gold bright on top. That contrast — warm gold against near-black silver — is the whole point of keum-boo, and it is worth reading our notes on oxidising and patina on silver before you dip the piece.
Everything you need for the bond — tweezers, burnishers and heat-proof holders — sits in our tweezers & soldering collection.