Richard Kornemann, conservator at the Museum Shop, Ltd, uses 23K gold leaf for many things: picture frames he's restoring, for architectural elements, on furniture (such as a baptismal font), and signs. To see an example, look at the Museum Shop, Ltd's own sign, which has been out in the elements for 20 years. Note that the gold letters are still bright; they haven't browned at all. This is one of the best reasons to go to the expense of using real 23K gold leaf, which can save money in the long run; it doesn't turn brown, the way gold paint does, and therefore does not need replacement or repair. The gold doesn't need sealing, either, to last a lifetime.
This is a greatly simplified description of the process used to restore an antique frame. First we clean it well to remove dirt, dust and any loose pieces. If areas are missing, we can duplicate them in one of two ways: by making a mold of existing parts which are identical, then pouring and attaching the replacement piece to the frame; or by using a sort of carving putty and hand-carving an identical piece.
A very expensive rust-colored clay, the consistency of butter, is then painted onto the entire frame. The purpose is to smooth minor imperfections, and several coats may be required.
A special adhesive called "sizing" is then painted onto a small portion of the frame, which is allowed to dry for 1-1/2 to 3 hours (depending on room temperature and humidity), until it is tacky. Care must be taken to only apply sizing to an area that can be gold leafed before the sizing dries. Then the 23K gold leaf is applied. When it goes onto a plain, flat part of a frame it often goes on unbroken. You may notice, in such an area, that there are visible lines in the gold every 3" or so; those indicate the individual sheets of gold leaf and are actually considered the mark of a fine, real gold frame. (If you examine average-priced gold frames, you will see that they do not have such lines because they are painted.)
When applying leaf to carved, ornate parts of frames, the gold crumbles into little bits, often almost a powder, and these areas may require many layers of leaf, requiring a lot of time and a lot of gold leaf.
A sealer is not required. The results are spectacular! Real gold has a patina like nothing else.
The traditional method of making gold leaf is by gold being hammered by hand until it is thinner than tissue paper. It is trimmed into 3-3/8" sheets and will blow in the slightest breeze, so requires great skill to handle. Special tissue paper is placed between each sheet of gold so it may be handled by the tissue.
Gold leaf is priced the same as gold on the world markets and it is necessary to check the price daily.