How to Apply Gold Leaf to Pottery
Gold Leafing, or mechanical surface gilding, is a technique of bonding thin sheets of pure or nearly pure gold to a surface. The gold leaf itself is an interesting material to work with and may redefine your concepts of the word thin. Each sheet of gold leaf is only 1/10,000 of a millimeter thick or put another way, a stack of 10,000 sheets of gold leaf would have the thickness of a dime! Gold leaf is sold by the book, and a book contains 25 leaves. The standard size for a gold leaf is 3 3/8" x 3 3/8". A book will cover about 1 1/2 square feet. There are two types of books sold, transfer and loose. Transfer books have the leaf attached to a piece of white tissue making it easier to handle if it is windy or if precise overlapping of the leaves is called for. Loose books have each leaf separated from the others by a page of saffron coloured tissue paper. I prefer the loose books. The kind I use is 23 or 24 karat, and is made by a company in Florence called Giusto Manetti
, which has been in the gold leaf business since the early 1800s.
Mechanical surface gilding involves the use of a special adhesive called gold size. Gold size is a viscous liquid made of 50% nonvolatile ingredients like phenolic resin, ester gum, tung oil and linseed oil, plus 50% volatile ingredients like turpentine. There are two types of gold size. The standard, which is ready for gilding after 10-12 hours, and the quick dry, which is ready for gilding after 1-3 hours depending on temperature and humidity. I prefer the quick dry. An even coat of gold size is brushed onto the surface and allowed to begin drying.
Successful gold leafing is knowing exactly when the size has dried to the correct tack (degree of stickiness) and is ready for the leaf. To test tack readiness, touch the surface with your knuckle and listen for a slight tick sound as you pull it away from the surface. The size should be dry enough that it is no longer in a liquid state, but still sticky to the touch. The key to getting a rich, gold surface is to apply the leaf when the size has just the right amount of tack. If it is applied too soon the size will force its way into the leaf and give it a mushy look. If it is applied too late the leaf will not adhere properly. With a bit of experience you'll get a feel for the timing. It usually takes at least an hour for the quick dry type size to reach tack readiness. It will adhere best to glazes and surfaces that have a very slight texture or tooth, like a matte glaze. The surface must be free of dust and grease.
The application of the gold leaf should be done in a calm atmosphere both the room and yourself! The slightest draft in the room, even your own breath, will send the fragile leaf flying. Traditionally, the leaf is transferred out of the book and onto the surface with a gilding brush. This is a soft, broad brush made of camel hair or sable. You stroke the brush through your hair a few times to give it a static charge and then the brush is held over the gold leaf. The leaf will jump up to the brush because of the static charge and it can then be lifted to the prepared surface and smoothed into place with the brush. A good quality artist brush can substitute for the more expensive gilding brushes. I prefer to lift and move the leaves with two pairs of tweezers and then use a brush to smooth the gold leaf onto the surface.
A day or two after the gold has been applied, the size will be thoroughly dry and the gold can be gently burnished with a cotton ball or piece of plush velvet. This will bring out the true luster and brilliance of the gold. Because the gold leaf is so thin, its colour is affected to some extent by the colour of the background surface. I usually apply at least two layers of gold to get a deep, rich colour. The second layer is applied a day after the first.
Other metallic leafs are available such as silver and variegated compositions. Silver leaf will tarnish so aluminum leaf is often used when a silvery look is needed. Aluminum does not have the warm look of sterling, but it is inexpensive and will not tarnish.
Gold leaf supplies may be found in a very well stocked art supply store, but you are more likely to find supplies at a sign painter supply business since it is sign painters who use gold leaf on a regular basis. Prices vary, but a book of loose gold leaf would typically be about $50.
Gold leaf is very durable its main commercial uses are for outdoor signs and truck lettering, but I would not recommend it for pottery that will be used in an oven or dishwasher, since these environments may affect the bond of the gold size. It is especially effective on the outer surfaces of jars, vases, teapots and such. It has a rich, lustrous depth to its appearance that is different from gold luster which is painted on and refired.
Give it a try!
This is page one of two. There are examples of finished works on my Gold Leaf