Numismatic and History Discussion Forums > Coin Photography, Conservation and Storage
Making plaster casts of coins
Obryzum:
This weekend I experimented with gilding some plaster casts with gold leaf. I used an oil-based gilding method, which is much simpler and faster than water gilding, but the results are never quite as good.
The results were decent -- about what I was expecting. I will post some pictures in a few days (I am still experimenting and I want to see if I can improve!).
It is a coincidence that casata137ec raised the question about seals. In order to gild anything, you need to seal the plaster with a skin. The gold sticks to the size, the size sticks to the skin, and the skin sticks to the plaster. If you put the size directly on the plaster, it just soaks into the plaster like a sponge and never gets sticky.
In my experiments I created skins using a variety of techniques. I tried diluted acrylic paints, diluted oil paints, diluted oil paints mixed with a medium, and just plain Liquin. The best results from my first batch of gilded coins was from the Liquin.
If you are not gilding and you just want something that looks good, the acrylic paints were great. It is very easy to dilute them, and they dry very quickly. That means you can put on several ultrathin layers in less than 30 minutes. The layers are so thin that they do not affect the details. The details become much more visible with the paint compared to white plaster. I will include some pictures of painted coins when I make my next batch . . . .
jamesicus:
--- Quote from: Obryzum on May 17, 2009, 09:36:39 pm ---This weekend I experimented with gilding some plaster casts with gold leaf. I used an oil-based gilding method, which is much simpler and faster than water gilding, but the results are never quite as good.
The results were decent -- about what I was expecting. I will post some pictures in a few days (I am still experimenting and I want to see if I can improve!).
It is a coincidence that casata137ec raised the question about seals. In order to gild anything, you need to seal the plaster with a skin. The gold sticks to the size, the size sticks to the skin, and the skin sticks to the plaster. If you put the size directly on the plaster, it just soaks into the plaster like a sponge and never gets sticky.
In my experiments I created skins using a variety of techniques. I tried diluted acrylic paints, diluted oil paints, diluted oil paints mixed with a medium, and just plain Liquin. The best results from my first batch of gilded coins was from the Liquin.
If you are not gilding and you just want something that looks good, the acrylic paints were great. It is very easy to dilute them, and they dry very quickly. That means you can put on several ultrathin layers in less than 30 minutes. The layers are so thin that they do not affect the details. The details become much more visible with the paint compared to white plaster. I will include some pictures of painted coins when I make my next batch . . . .
--- End quote ---
I am a long time Calligrapher and for many years now have used Titanium White (Winsor & Newton Atists' Acrylic colour #349) for flat gilding (versus raised gilding on gesso). I use a thin mix and paint one coat over the area to be gilded -- it is much easier to use than egg-white glaire. The gold leaf adheres very well to the Titanium paint and can be burnished to a high lustre if desired. I have used other makes besides Winsor & Newton with equally good results. You may still have to skin the plaster using Liquin before applying the acrylic paint.
James
maridvnvm:
I bought a set of uniface plaster casts of some mid to large bronzes some years ago. Busts etc. that I will never own. They had been painted to imitate various patination. Some of the paint has flaked in some areas but they are good enough to give you the idea.
Here is one of them (a large Probus, just under 43mm, and the reason that I bought the lot). The remainder can be seen in the following gallery.
https://www.forumancientcoins.com/gallery/thumbnails.php?album=1007
Regards,
Martin
jamesicus:
--- Quote from: jamesicus on May 17, 2009, 11:44:44 pm ---I am long time Calligrapher and for many years now have used Titanium White (Winsor & Newton Atists' Acrylic colour #349) for flat gilding (versus raised gilding on gesso). I use a thin mix and paint one coat over the area to be gilded -- it is much easier to use than egg-white glaire. The gold leaf adheres very well to the Titanium paint and can be burnished to a high lustre if desired. I have used other makes besides Winsor & Newton with equally good results. You may still have to skin the plaster using Liquin before applying the acrylic paint.
James
--- End quote ---
Not the best exemplar, but I used Titanium White to flat gild this versal "A" (not burnished).
James
Obryzum:
I spent the day making a mess, but it was fun. Before I started experimenting with the coins, I had only tried to gild something once before. I need a lot of practice. Here are the early results.
A word about the results -- the final product looks much better life size. These larger pictures show all the warts, all the flaws.
What I learned: The hardest part is making a good skin. When making a skin, it's a game of tradeoffs. The plaster is very porous and you need to get it sealed. If you do not seal it, the gold size (which is the "glue" that you paint on and that makes the gold leaf stick to the surface) soaks into the plaster and the surface does not get sticky. You can get a better seal and better adhesion with more coats, but more coats means sacrificing more detail. I had the best results using medium yellow for the base coat to create the skin. I tried titanium white but I lost too much detail. As anyone who had painted before knows, there is a world of difference between the different colors. Medium yellow is a good choice because it goes on evenly (even when watered way down) and dries fast. After the yellow base coat I added one coat of Liquin. Then I gilded it with patent gold leaf, which is much easier to work with than loose gold leaf. The gold leaf is supposed to be 22k gold, but according to my acid tests, it is probably closer to 20k. As you can see, there are a few tiny spots where the gold did not adhere. I took that picture when it was overcast outside so the gold does not look very gold. To help mask some of the flaws I decided to add some fake "patina" by holding it in a candle flame and getting some soot on the surface. Then I rubbed off the soot and took the final picture. The sun had come out so the color is much better in the last photo.
I used the oil gilding method, so this cannot be burnished to shine and reflect. I am too much of a beginner to try water gilding yet. But I will keep practicing. For now I think the best way to improve the final results is to try to make a better quality plaster cast.
My goal is to be able to make a display of my gilded casts so that I can enjoy my coins more -- even while the real ones are locked in the safe.^^
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