Whilst looking for photos of my polydactyl cat, I ran across these and decided they needed to see the wide open spaces of the interwebs.
I had to "make up" some missing ornaments, as there was only the one, and it was gone, but if you study frames, ornamentation is a language, that once learned, makes it relatively easy to fill in the missing "words". Of course, it took some time to learn the language. Just looking at frames is a start; then there are the classics; "The Grammar of Ornament", Owen Jones, and "The Encyclopedia of Ornament", A. Racinet. Both have modern reprints. Obtaining a catalog from Decorators Supply, in Chicago, is worth the price of admission, though not focused on framers needs.
The easiest method of identifying what kind of gilding one is looking at, is to look for the leaf lines; the spot where the leaves meet. In the above sample, the arrows are pointing at the lines of metal leaf (schlagmetal, dutch metal, composition leaf). When it is "gold" colored, it is a brass alloy, about 10,000th of an inch thick, and comes in a 5 1/2 inch square leaf. There are aluminum leaves; silver colored; copper leaf; copper colored, and various kinds of variegated leaf; multiple colors in one leaf.
Here, the leaf lines on matte, karat gold. The leaves come in slightly different sizes, depending on manufacturer, but are close to 3 1/4 inches square, and about 300,000th of an inch thick. This is the most common form of karat gold, though there is ribbon or roll gold, and there is a wide variety of karat weights and gold alloys, ranging from a white gold at 12K, to pure 24K leaves. For outdoor use; all those domes and statues, use a minimum of 23K. Another way of identifying genuine gold on picture frames, would be a distinctive difference between high spots and recessive areas of the frame, where the high spots have been burnished to a mirror like shine. This is called matte and burnish work, and requires the gold to be laid in the water gilt method, over a material called bole. Bole is mixed with glue, applied in multiple layers to the frame, polished, then gilt. When dry it is burnished with an agate stone, the most popular stone for burnishing. Bole comes in reds, yellows, blues, and blacks, with multiple shades in each color, and can often be seen where the leaf is worn, either through age or intention.
This is a brief explanation of what one is looking at; but this is a very ancient craft, and I touch on only the more common styles. There is gilding with tin foil; silver leaf lacquered to look like gold; bronze powders; bronze powder paint; and now, the non-tarnishing mica powders.
Size gilding, water gilding, glass gilding, engine turned gilding, and not least, gilding the lily. 8-)
And just to confuse the issue, there are many examples of lesser materials carefully finished to look like genuine gold.
Addendum: Metal leaf comes in other sizes as well, 6 1/4 square being the other common size.
Two images showing the way I handle karat gold leaf. Top, the tip is held by the last two fingers of the right hand for cutting the leaf; bottom, the knife is now held by the last two fingers of the left hand. I work directly from the book of leaf. A book of leaf holds 25 leaves, between a tissue paper. I used to just insert a piece of mat board under the tissue, as a "cutting board" for cutting the leaf, but on a "bad day", this could be difficult with the mat board and the book all wanting to go in different directions. I've added a little touch that helps, though; double sided tape, framers ATG tape, holding the book to the mat board. I've used packaging tape as a surface on the mat board. The knife is one of the small, swiss army type knives, with a stainless steel blade; I've found they are the easiest to maintain a good edge on for cutting leaf. (The sign maker I worked with when first learning karat gold work, used the elongated fingernail, of his right hand, as a "knife". I did for a while, but kept breaking that nail.)
I'm patching "holidays, missed spots, holidays, get it" from the initial size gilding, so there is some cutting.
In the bottom image , on the back of my left hand, some small specks of gold adhering to the minuscule amount of Vaseline on the back of my left hand, rubbed in there to provide a place for me to pick up a little tack for the tip, so it can pick up the leaf. Cut the leaf to the size needed, brush the back of my left hand with the tip, (flat, long haired brush for handling leaf) to get some tack to it, pick up piece of leaf, and apply. In an earlier post, where I'm speckled, when gilding I'm usually "glittery", as I use the right front of my shirt to clean and dry the tip.
On size work, I usually work with the book, almost like "patent gold" when I can, rolling the leaf onto the surface directly from the book. No tip, no knife. Patent gold is a leaf slightly affixed to a sheet of paper that can be laid on the surface being gilt; useful for outdoor applications, as loose gold leaf is incredibly fragile.
Metal leaf, another post. And an aside, these are my techniques for an ancient craft, and they are not necessarily definitive.