The Stages of Gilding

Before the gold leaf is applied there are several stages of preparation that the surface to be gilded must go through. The gilded surface shows any imperfection in the underlying layers so diligence is required in the preparation to achieve the best results.

The stages of gilding a surface are:

• sanding the timber

• applying a size coat

• applying any intelaggio

• applying gesso

• recutting and polishing

• applying bole

• gilding

• burnishing

• sealing and toning

Some of these stages can be omitted depending on the type of gilding that you are doing. The stages prior to gilding are to prepare the surface to a flawless state.

Sizing

The first layer in the gilding process is the size coat. The sizing is done to isolate the timber from the gesso. Without the size coat the timber could draw out the binder from the gesso causing it to flake off.

Size can be made by boiling parchment clippings in water and straining the resultant mixture to form a solution that will set like jelly when cold. Another method of making size is to soak rabbit skin granules in water and then melt them over a double boiler.

Before the size is applied it is warmed and a small amount of whiting is added to give it a milky appearance and help it bond with the first layer of gesso. The size is then applied evenly with smooth brushstrokes to avoid making any bubbles. The surface must be covered completely and if the timber is absorbent or coarse grained, a second coat should be applied.

In the case of a jointed frame, the joints should be covered with intelaggio after the size has been applied. Intelaggio is a cloth reinforcement. Strips of cloth are glued over the joints to stop the gesso cracking if the timber moves.

Gesso

The next stage of preparation is the gesso layer. Gesso is a mixture of size and chalk. The Italians used gypsum instead of chalk and this is how the name gesso, Italian for gypsum, came about.

A mixture of size and chalk is mixed carefully to avoid bubbles until it is the consistancy of a flowing cream. Sometimes the addition of slaked plaster is made to give a harder finish. If the gesso cools down it can be warmed either by placing it in a double boiler or by standing the container in some warm water.

Note: Do not keep the gesso over the heat source because it can cause bubbles to form in the mixture which then will appear as pinholes when it is dry.

The gesso is applied whilst warm with smooth brushstrokes. Several layers are required to build up an adequate surface. Each layer must be applied as the last layer just sets and becomes dull. If the layers are allowed to dry between application, the layers can delaminate and flake off.

Note: Each layer of gesso should not contain more glue than the last layer, so an addition of a spoonful of water to the mixture between layers is advisable.

If the subsequent layers are stronger than the ones underneath, the gesso can curl up when drying and pull the previous layers off.

Note: Always make more gesso than you need. A larger quantity will keep warm longer without having to be reheated and you will avoid the risk of running out.

Recutting and Polishing

When the gesso is dry and hard, the surface must be cleaned and smoothed to remove any imperfections. The flat areas can be worked over with a cabinet scraper and any ornanments can have their details refined with recutting tools and chisels.

Following the recutting the surfaces are then polished with a damp cloth. The object of the polishing is to achieve a silky smooth surface.

Note: Be careful when polishing not to expose areas of bare timber beneath the gesso.

Applying Bole

Bole is the name given to a fine clay that gives both the gold its underlying toning and a cushion to accept the leaf. Traditionally the clay was ground with a mortar and pestle and then added to size to form a coloured mixture the consistancy of milk. It is now possible to obtain ready ground bole in a paste form called polliment.

Different colours of bole are used for different effects. Most commonly, yellow bole is used all over the frame and red bole is used on the highlights of the mouldings. The yellow colouring helps conceal any areas that are missed when they are gilded. The red bole gives a rich lustre to the highlights which are often burnished.

Up to six layers of bole may be required on the highlights but usually two layers of yellow bole are enough on the lowlights. Before applying the bole the surface must be dusted. The bole is applied with a soft brush that is either made from camel, squirrel or sable hair.

After the bole has been applied leave the frame for a day to harden. Any imperfections in the bole can then be rubbed off with 1000 grit wet and dry paper or a similar sandpaper. When the surface is perfect it is gone over vigorously with a bristle brush to polish it ready to gild. Some gilders polish the bole with agate burnishers as an alternative to using the bristle brush.

Note: If you are gilding the surface with schlagmetal, the bole can be substituted with an oil based enamel paint or other suitable colouring.

The surface is then ready to gild.

Gilding

Gilding a surface is applying a coating of either a gold leaf, a substitute gilt leaf, or a layer of gold paint. The most common form of gilding the picture framer encounters is schlaging. Schlaging is the name given to the application of an imitation gold leaf called schlagmetal or Dutch metal. In this section you will learn how to identify and apply the various different types of gilding.

Gilding with leaf can be divided into two main methods:

• oil gilding

• water gilding

Oil gilding can be done with fine gold leaf, schlagmetal and bronze powders.

Water gilding can only be done with fine gold leaf.

Oil Gilding

Oil gilding involves applying an oil based size to the bole layer to adhere the leaf to the surface. The size is applied and after a initial drying time the gold leaf is applied. The oil size dries to a state of tackiness that gives the leaf something to stick to.

Oil sizes are available pre-mixed from a variety of resins, oils and driers.

Each size has a specific "open time" which is the time taken for the size to reach optimum tackiness.

The most commonly used size is 12 hour size.

This allows the gilder to apply the size in the afternoon of one day and apply the gold leaf the following morning. The longer the open time of the size, the smoother the finish will be. The size flows and self levels over its drying time and thus the longer sizes have more time to flatten out.

There are times when a quick drying size is desirable, such as a small repair.

I have found the most effective "oil type" size for fine gilding is garlic juice.

The juice is extracted by blending cloves of garlic in the liquidiser with distilled water. The size is applied and allowed to dry thoroughly. When you are ready to gild all you need to do is breathe some warm moist air on the surface and the size is activated enough to allow the leaf to stick to the surface.

In the case of schlagmetal gilding the surface to be gilded must be sealed before the application of the gold size. This is necessary to isolate the schlagmetal because it oxidises when exposed to air and discolours.

You seal the surface with shellac prior to sizing.

When the size is just right ( you can test the tackiness of the size by running the hairs on the back of your hand across the surface, if you feel a gentle pull then the size is ready). It is better to wait longer than to gild onto a wet size. If you apply the leaf to wet size the finish will be poor and the size will not dry properly under the leaf... the leaf is applied to the surface and tamped down.

After 24 hours the gilded surface can be polished with a soft cotton cloth to remove any skewings. In the case of fine gold the surface is cleaned with a soft mop brush to allow the pieces of gold leaf to be collected.

Water Gilding

Water gilding is consider to be the true form of gilding. The techniques and results have been used for thousands of years.

Water gilding must be done on a well prepared surface of gesso and bole. The technique involves applying a coat of water or water, size and alcohol mix to the absorbent bole layer. The gold leaf is then layed on the wet surface. The bole absorbes the liquid and the gold adheres to the surface.

Specialised tools are required when gilding with fine gold leaf, they include:

• gilder's tips - thin flat fine brushes made from badger or squirrel hair

• gilder's cushion - to cut the gold leaf on

• gilder's knife - a long flat well balanced tool used for picking up and cutting leaf

• agate burnishers

The procedure for water gilding is as follows:

1. Prepare your moulding with size, gesso and bole.

2. Arrange your tools, gold leaf and gilding solution to allow them to be easily accessable.

3. Using the gilder's knife, place several sheets of leaf at the back of the cushion.

4. Pick up a leaf with the knife and lay it flat at the front of the cushion. The leaf can be coaxed by turning it over with the knife.

5. Cut the leaf into manageable pieces with the knife.

6. Using the tip pick up a piece of leaf and then transfer the tip to your cushion hand.

7. Holding the cushion in one hand with the gilder's tip between two fingers of the same hand, apply a wash of the gilding solution over the area you wish to gild.

8. Transfer the tip to your other hand and then place the piece of leaf on the wetted area. The tip should be parallel to the surface at this point. The surface tension of the water will pull the gold from the tip the moment the leaf touches the wet area.

9. If the piece is flat procede to apply another wash next to the first piece overlapping the edge of the first leaf by a fraction and then repeating step 7. If the piece did not lay successfully then remove it immediately with a wet brush and try again with a fresh piece of leaf.

10. After laying a couple of pieces you can go back and pat down the first piece to ensure that it bonds with the bole.

11. Repeat stages 6 - 10 until you have completed the frame.

12. After completing the frame go around it with a soft mop brush sweeping up any loose pieces of leaf.

13. Any faults can now be seen and rectified by applying additional pieces of leaf.

14. The best results are obtained if the moulding is gilded again. This is called double gilding. If you are going to double gild a piece you must avoid touching the surface between laying the first layer and the second.

15. The piece can then be set aside for a few hours prior to burnishing.

Burnishing

After the piece has sat for a few hours it can be burnished.

Burnishing is polishing the gold with a polished agate burnisher to make the gold shine as if it is solid metal.

The gilded surface can be matt or burnished and very often the best effects are where low areas are left matt and the highlights have been burnished.

To emphasise the matt effect the gold can be given a thin coating of shellac called ormolu.

The procedure for burnishing is as follows:

1. After waiting three hours from the time of laying the leaf, test a small area of the frame to see if it is ready for burnishing. To do this pass the burnisher over the surface applying only gentle pressure. If the burnisher runs smoothly then you can procede to apply more pressure. The burnisher should leave a polished trail in its path.

2. When the surface is ready, procede to burnish the surface all over using appropriate sizes of agate burnishers. It is best to burnish the frame evenly rather than working excessively in one particular area.