Water Gilding vs Oil Gilding: Which Method, and When

Choose oil gilding for exterior work, architectural details, signage, monumental lettering and any project where durability or a more direct application matters. Choose water gilding for interior frames, furniture, carvings and restoration work where you need a traditional ground that can be burnished to a mirror finish.

Both methods lay metal leaf onto a prepared surface, but they use different grounds and different adhesives, and that choice governs where the finished piece can live, how it will look, and how much preparation it will take to get there.

Oil gilding uses an oil-based gold size brushed thinly onto a sealed, smooth surface and left until it reaches the correct tack. The leaf goes on while the size is still open. Traditional water gilding is a layered system: a gesso ground, then coloured bole bound with animal glue, reactivated with water immediately before the leaf is laid. Once fully dry, the gold can be polished with an agate burnisher.

One distinction worth making early: traditional water gilding is not the same as applying leaf with a modern water-based acrylic size. Systems such as the Kölner Instacoll range are genuinely useful for interior decorative work and can produce a bright, near-burnished finish with far less preparation, but they do not build the gesso-and-bole ground that traditional water gilding depends on. They are a third route rather than a shortcut to the second.

Oil gilding: what it is and when to use it

Oil gilding, sometimes called mordant gilding, uses a drying oil-based adhesive to hold the leaf. It is the only sensible choice for exterior work or damp conditions, and it covers most professional and decorative projects: exterior lettering, monumental inscriptions, architectural details, shopfronts, weathervanes, gates, narrowboat panels, furniture and decorative objects. It works across properly prepared stone, metal, sealed timber and other stable surfaces.

It is not, however, a forgiving method in the way that people sometimes assume. Oil size will not hide brush marks, dents, open grain, dust or a poorly filled repair. Genuine gold leaf is roughly one 250,000th of an inch thick, so every defect beneath it stays visible after gilding, and every pool of size stays soft. Where size collects in a carved recess or a moulding, the leaf sinks into it and loses its lustre completely.

Start with a sound substrate, complete repairs, and apply a suitable primer or sealer. On stone, seal with a transparent sealer or a gloss enamel so the surface stops absorbing size, you may need more than one coat, and it must dry hard before you go any further. Sand smooth, remove all dust, and make sure the surface is clean and grease-free.

Apply the size thinly and sparingly, making sure every surface is evenly coated with no puddles anywhere. For flat work and wide moulded bands, a flat ox hair filling-in brush in series 1392 is the right tool, and masking tape will define the edges cleanly. For carved narrow mouldings, a round brush in good hog hair works better.

For exterior gilding, the primer, size and leaf all need to suit the substrate and the exposure. Use 23.5ct genuine gold leaf or above outdoors, anything lower in carat will tarnish in the weather. Our fuller guidance on exterior work is in gilding on stone.

Water gilding: what it is and when to use it

Traditional water gilding is the method behind polished frames, carved furniture, statuary, icons and historic interiors. It takes considerably more preparation than oil gilding and rewards it with a depth and reflectivity that oil size simply cannot reproduce.

It suits picture and mirror frames, carved interior woodwork, furniture, statues, religious artwork and conservation projects. It comes into its own when a design needs both matt and burnished passages, or when the colour of the bole is part of the finished effect rather than something hidden beneath the gold.

The surface is built in layers. Timber is sealed, then coated with several layers of gesso, which is levelled, shaped and polished until it is extremely smooth. Bole goes over the gesso. Immediately before the leaf is laid, the bole is wetted with water or gilding liquor, which softens the glue just enough for the gold to bond. Once everything is thoroughly dry, selected areas can be burnished, the agate compresses the ground beneath the gold and brings up a mirror-like shine.

Water gilding is unforgiving of rushed preparation in a way oil gilding is not. Uneven gesso, sanding scratches, tool marks and poorly applied bole all become more obvious after burnishing, not less. The quality of the finished surface is decided long before any gold is laid.

It is also permanently sensitive to moisture. The water that makes the method possible is the same water that rules it out for exterior use: traditional gesso and animal-glue grounds stay water-responsive for life. Learn the technique on small test panels before committing to carved or valuable work.

Preparing a gesso and bole ground

Preparation is the whole process of water gilding. The ground has to be smooth, stable, and able to take both wetting and burnishing.

1. Prepare the substrate

Timber should be dry, stable and free from wax, oil, dirt and loose material. Finish repairs and refine carved detail before any gesso goes on, because the gilding will reproduce the surface beneath it rather than disguise it.

2. Size the surface

Traditional preparation begins with a dilute animal glue, usually rabbit skin glue, which penetrates and seals the timber and gives the gesso something compatible to key into. Soak the granules and warm them gently; never boil them, and keep tools and containers clean.

Isinglass, a refined fish glue, is the other specialist adhesive used in fine gilding and conservation. Which glue and what concentration will depend on the object, the materials already present, and the method you are following.

3. Apply the gesso

Traditional gesso is whiting or a suitable chalk combined with warm glue size, applied in multiple thin coats with a proper string-bound gesso brush. Avoid beating air into the mixture, which causes pinholes. On carved work, carry the material into the detail without filling or softening it. Once dry, level and smooth the gesso, abrasives on the flats, suitable scrapers around ornament.

4. Apply the bole

Boles and clays form the coloured ground beneath the leaf. Some are supplied ready to use; others need an appropriate glue binder. Our Sinopia clay boles for water gilding cover the traditional range.

Colour matters more than it first appears. Red gives a warm, traditional character and shows through attractively where the surface is distressed or the gold wears. Yellow softens small faults and reads lighter. Black, white and the other colours are used to achieve particular effects beneath gold, silver or palladium. Apply the bole in controlled coats and refine it thoroughly, it has to provide both the colour and the surface that makes clean burnishing possible.

Gold size: grades, open times and reading the tack

The most common oil-gilding mistake is laying the leaf when the size is either too wet or too dry.

Oil sizes run from quick-drying grades ready in an hour or less, through to slow grades of twelve hours or more. Lymmit, Japan, Le Franc and One Shot all sit within our gold size range. Faster sizes suit small areas and simple lettering; slower grades give you the working time that large surfaces, carving and complex jobs demand. For gilding on stone, most gilders reach for Lymmit 1-hour tinted size, the yellow ochre tint shows exactly where the size has been laid, and any small miss blends in rather than showing as a bare patch.

Treat the stated hour as a product classification, not a countdown. Temperature, humidity, airflow, film thickness, dilution and substrate porosity all change how quickly a size reaches tack and how long it stays open, which is why the test has to be repeated on every job rather than assumed.

Lay a test area in the same conditions as the work itself. As the size dries, the wet shine dulls slightly. At the right moment it should feel tacky without transferring anything, the dry tack of a post-it note is the comparison most gilders use. Test with the back of a knuckle, or the pull on the fine hairs of the back of your hand, rather than a fingertip, which will leave a print in the size.

Too early, and the leaf sinks in, wrinkles, dulls and can look greasy. Too late, and it will not bond consistently, leaving faults and bare areas. Break larger projects into manageable sections, and keep the sized surface out of the dust while it comes to tack, standing the object vertically or tenting it with paper both help.

Applying the leaf, and correcting faults

Loose leaf and transfer leaf call for different handling, and most gilders end up with their own variation on both.

The traditional studio method for loose leaf has not changed in centuries. Transfer the gold from the book to a gilder's cushion, flatten it with a soft blow of breath, and cut it with a gilder's knife. A gilder's tip, drawn lightly across the bridge of the nose to pick up the faintest trace of grease, will then lift the gold to the work. Signwriters working at speed often skip the cushion entirely, cutting with a fingernail while holding the book in one hand and the tip in the other.

Transfer leaf is adhered to acid-free tissue, so no cushion, knife or tip is needed. Hold the tissue by its border, lay the gold face down onto the sized area, rub the back of the tissue gently with a finger or soft cloth working away from the border you are holding, then peel the tissue slowly away. Overlap each subsequent sheet by about 3mm. Transfer is ideal for flat surfaces; anything intricate needs loose leaf.

When the surface is covered, a squirrel hair gilder's mop tidies the work and brushes away the excess. Those offcuts, skewings, are worth keeping. They can be reused, or sold back to the gold leaf manufacturer for recycling, which is a small but real offset against the cost of genuine gold.

Missed patches are called faulting, and they are easy to see over a coloured ground but harder over a tinted size. Cut small pieces of loose leaf to patch them. If the size is nearly dry, breathing gently over it will usually bring back enough tack to take the gold; if it has cured completely, apply a little fresh size, preferably a clear one. What you should not do is brush a second full coat of size over dried size and gild again, the finish will not match. Remove the dried size with white spirit instead, keeping clear of the gilded areas, then clean, dry and start that section afresh.

Burnishing, and why water gilding cannot go outdoors

Burnishing is the strongest single reason to choose water gilding. Once the leaf and the ground beneath it are completely dry, an agate tool passed over the surface with controlled pressure compresses the ground and brings the gold to a bright, reflective finish. Combining burnished and matt passages on the same piece is what gives traditional frames and carved detail their depth.

Oil gilding has no compressible gesso-and-bole structure to work against. Oil-gilded leaf can be cleaned and finished carefully, but taking an agate to it damages the surface rather than polishing it. Agate burnishers belong to water gilding, and only once everything beneath the leaf has fully dried.

The same moisture-responsiveness that makes burnishing possible is what keeps water gilding indoors. Exterior exposure leads to swelling, cracking, loss of adhesion and eventual failure beneath the gold. Varnishing over the top will not rescue it - a coating cannot correct an unsuitable ground, and it will alter the colour and brilliance of the gold in the attempt. For anything outdoors, use a properly specified oil-gilding system and 23.5ct leaf or above.

Once work is finished, our guide to gold and metal leaf care and maintenance covers cleaning and long-term protection for both methods.

What you need for each method

For oil gilding: a suitable primer or sealer for the substrate; abrasives and clean lint-free cloths; an oil-based gold size; a clean flat ox hair brush in series 1392, or hog hair rounds for carved work; genuine or imitation leaf suited to the job; a gilder's cushion, knife and tip if you are using loose leaf; a squirrel hair mop; white spirit for corrections; and safe disposal arrangements for oily materials.

For traditional water gilding: stable timber or another suitable interior substrate; rabbit skin glue or another specified glue; whiting or prepared gesso; string-bound gesso brushes; scrapers and fine abrasives; bole or gilding clay; gilding water or liquor; loose genuine gold leaf; a gilder's cushion, knife, tip and mop; and agate burnishers.

The exact list shifts with substrate, scale and finish. Restoration work should follow the object's existing construction wherever possible. Both methods are covered in depth in Practical Gilding by Peter and Ann Mactaggart and Gold Leaf Techniques by Kent H. Smith, available in our gilding books and DVDs.

Choosing between them

Oil gilding is the answer when the work will be outdoors, when the substrate is stone or metal, when the job is signage or monumental lettering, or when you need a durable finish by a comparatively direct route.

Water gilding is the answer when the piece stays indoors and the quality of the surface is the point - a burnished finish, a traditional frame, a carved object, or restoration work where the original ground was water gilded and matching it matters.

For straightforward interior decorative projects that do not warrant full traditional preparation, an acrylic size sits usefully between the two: quicker, easier to clean up, capable of a bright finish, but not a gesso-and-bole system and best not described as one.

Whichever route you take, test the complete system before you commit. Preparation, tack, leaf and finish behave as one thing, and every problem is far cheaper to find on a sample than on the finished object.

Frequently asked questions

What is gold size?

Gold size is the adhesive that holds the leaf to the surface. Oil-based sizes are graded by drying time, from an hour or less up to twelve hours or more, and are the only option for exterior or damp conditions. Water-based and acrylic sizes are for interior work.

What do I need to start gilding?

At minimum: a gold size, leaf, a brush to apply the size, and a gilder's mop to tidy the work. Loose leaf also needs a cushion, knife and tip; transfer leaf does not. Our gilding starter kits bring the essentials together.

Can water gilding be used outdoors?

No. The traditional gesso and animal-glue ground stays water-responsive permanently, so exterior exposure causes swelling, cracking and loss of adhesion beneath the gold. Varnishing over it does not solve the problem. Use oil gilding with 23.5ct leaf or above.

How long does gold size stay open?

The stated hour tells you roughly when it becomes ready, not how long it lasts. Most oil sizes then stay workable for several hours, but temperature, humidity, film thickness and substrate all shift the window. Test on the day rather than relying on the grade.

Does gilded work need sealing?

Genuine gold does not tarnish and generally needs no sealing, though exterior work benefits from correct specification from the outset. Silver, copper and imitation leaf all tarnish and must be sealed. Burnished water-gilded surfaces should not be varnished, as it destroys the finish.

We have supplied specialist gilding materials to professional gilders, restorers and decorators since 1840. If you are unsure which method or which size suits your project, talk to our team, or browse the full gilding range to get started.