This section deals with the different oil sizes that are available to gild with.
To adhere the metal leaf to the surface, and adhesive size is used. There are many different types available and each has their own distinct properties. Oil-based sizes are provided with a guideline ‘open-time’. That is to say a ‘1-hour size’ can be gilded up to an hour after the size is applied, whereas a 20 hour can be gilded up to 20 hours later. Size one day, gild the next so to speak. However, it must be noted that temperature, humidity, surface and many other factors will reduce or prolong the open-time of size. Only experience and experimentation will provide the best time to gild an object.
Oil sizes are applied by brush and left to dry until the required amount of tackiness is achieved. If left too long however, the size will dry and a fresh application over the previous layer will need to be made. The closer to the size drying out that you can get will usually produce a shinier finish. It is important that this is done in a dust free environment as any contaminants in the air will stick to the size and mar the final finish. Being turpentine based, brushes should be washed out in turpentine. If the gold is applied too early, a matt finish is made. This can be used as an effect all in its own right and can help to convey proportional values to an artistic piece. However, because the size is not set enough, the gold can easily be scratched off the surface, even many days after the piece has been gilded.
Even though it is called oil gilding, there are water-based sizes available. These are milky in their appearance but dries clear. The size is applied and will usually be ready to gild on in just 10-15 minutes. The main difference here however is that it remains open indefinitely. However, after too much time, dust and contaminants will render the surface unusable. Although the finish will not be as brilliant as high open time oil sizes, it is a quick and easy product to use, has a long open-time and its simple to clean brushes out in soapy water after use. Great for the beginner!