There are several reasons enamels crack. The most common reason enamels crack is there is not enough counter enamel on the jewel. Counter enamel is enamel on the back side of the jewel. Your base metal expands as well as the enamel when heated, and contracts when cooled. Without enamel on both sides of your base metal one side is going to expand more causing the opposite side to crack. If enamel is placed evenly on both sides of the metal you can eliminate this cracking. Sometimes this happens as it is cooling, when this happens there is very little enamel on the back. But I have seen the enamel crack years later when the enamel was not even on both sides of the base metal.
In some cases you can also dome a piece of metal and use less counter enamel as in a bead. But if you plan to put a thick layer of enamel on the front of the metal you then need more counter to avoid cracking.
Another reason enamels crack is if you use a hard firing enamel next to a low firing enamel. Hard firing enamels take longer to fire, and low firing enamels take less time to fire. Great reason the make test plates and see when each enamel melts first when they are all fired at the same time on the same plate. You can see on my test plate dot #4 is still grainy while the others are smooth. So #4 is a harder firing enamel and if placed next to #5 and you fired it long enough that both enamels were smooth in time the jewel will crack.
Cracking takes place in leaded enamels as well as unleaded enamels. Unleaded enamels are harder firing enamels than leaded enamels so if you combine them on the same jewel you can experience cracking. If you need to use them together use the unleaded first then layers of leaded to avoid cracking.
Many enamelist have difficulty using warm colors. There are a couple of things that help.
First start with a hard firing flux. Flux is the base coat, it is like a primer used in painting. It keeps the enamel away from the metal, as many are not compatible with the metals we use to enamel on. The hardest leaded enamel for silver is Bovano’s #3. For Gold it is #2 And for copper is # 1
Bovano flux #3 also has a blue base tint that does not turn yellow. I have noticed in some manufactures flux for silver, if accidentally fired too high will turn yellow. With a hard fire enamel flux the warm colors are less likely to come in contact with the base of fine silver, gold, copper or sterling silver. When you are firing too long or too high the base gets hot = the fine silver and holds the heat. Then the flux gets liquid and the color layer you are firing mingles with the flux coat and eventually comes in contact with the fine silver = a phlegmy looking yellowy brown= burnt enamels. So if you fire a bit lower temp, the flux will not get liquid as you only need to melt the top layer of color. Your color enamels are lower firing enamels =melts faster than your flux. So you need to choose the temperature and firing time just enough to melt the last layer you have applied.
In the technique, you will also know you are over firing, if your enamels are climbing up the walls of your cloison wires. And think about that. If your enamel is climbing up the wires that means you have less flux at the base. So now your warm color is closer to touching the fine silver and burning.
I only want to fire my warm colors a couple of times. With too many firings they burn out and get dull. To help with this I use the flux in the cells of the warm colors each time I fill the cells of my cool colors until it is at my last several layers. Also just in case I crack the piece in setting or it was dropped or damaged in the future I will have the opportunity to re-fire the jewel without my colors burning out.
There are some warm colors that have ash or blue bases and will not burn as easily.
If you do test plates you can see this, such as Ninomiya H24 and N26, yellows with ash bases. Oranges also, look at the test and you can see it has an ash base, like Ninomiya N21. It is not as bright of an orange but if you put N24 first then the N21 this brightens your orange and you will not have to worry about burning.
You really have to do the test plates and analyze the colors. On my pink color plate with 14 colors I can see some have a yellow base and some have a blue base. Use the blue base first then the yellow base one to get a brighter color, in the same color family. Do color plates and use all your warm colors, one of all reds and one of all yellows, and fire several times to see which of the reds and which of the yellows burn first. Then you really know which can handle more firings. It takes time but when it is all over you will be very confident of the end result.
Fluxes for transparent and medium firing enameling. Firing time varies on the size of your jewel. I work small and like to start around a min and go up in seconds. Just a quick peak in the kiln at eye level you can see if the enamel has fused.
What is flux? it could be thought of as primer when you are painting a wall, or gesso on and oil canvas. It is a base coat of enamel that allows enamels of a wide range of physical properties to be use in this technique and not burn.
Fire at 1450 and up to 1550 degrees
Thompson’s Unleaded 2030 Flux. Here is a link to Thompson’s Color Chart of Opaques for Copper
Thompson’s Color Chart of Transparents for Copper
Ninomiya’s Leaded L11 Flux Here is a link to Enamel Works Color Chart of Opaques for Copper
Enamel Works Color Chart of Transparents for Copper
Enamel Works Color Chart of Opalescents for Copper
Bovano’s Leaded #1 Flux You can down load their color chart here,
Bovano’s Color Chart of Opals, Opaques, and Transparents for Copper
I make enamel and cloisonne jewelry. And Fine Silver is my choice of metals. The weight of the jewel as well as the strength is a factor and in choosing the gauge of the fine silver. For pendants I prefer 20 gauge and for earrings 22 gauge.
Fire at 1425 – 1450 degrees
Thompson’s Non Leaded 2020 medium firing or 2040 for a hard firing fluxes. In my work I like a hard firing flux on my bases. Here is a link to Thompson’s Color Chart of Opaques For Fine Silver
Thompson’s Color Chart of Transparents for Fine Silver
Ninomiya’s Leaded N1 Flux Enamel Works Color Chart of Opaques for Fine Silver
Enamel Works Color Chart of Transparents for Fine Silver
Enamel Works Color Chart of Opalescents for Fine Silver
N3 = Leaded pre – washed flux
G 110 Leaded hard flux
Bovano’s Leaded #3 this is a hard flux with a blue base, this is my favorite flux on fine silver.
Bovano’s Color Chart of Opals, Opaques, and Transparents for Fine Silver
Thompson’s Non Leaded 2040 flux. Thompson’s Color Chart of Opaques For Silver
Thompson’s Color Chart of Transparents for Silver
Ninomiya Leaded N1 or N3 Flux Enamel Works Color Chart of Opaques for Silver
Enamel Works Color Chart of Transparents for Silver
Enamel Works Color Chart of Opalescents for Silver
Bovano’s #3 Leaded Flux, both of these are hard enamels and I think it is helpful in keeping the surface contamination down of the sterling silver away from the layers of enamels.
Bovano’s Color Chart of Opals, Opaques, and Transparents Silver
Fire at 1425 – 1450 degrees
Bovano Leaded #2 Flux and a link to, Bovano’s Color Chart of Opals, Opaques, and Transparents for Gold
Fire at 1250 Degrees – 4-8 min.
Low to Medium expansion Enamels Thompson’s Color Chart of Opaques for Stainless Steel
Thompson’s Color Chart of Transparents for Stainless Steel
Ninomiya’s Leaded N4
Bovano’s Leaded 619
Brass Today is Gilded Metal
Today many are asking about enameling on brass. It needs to be gilded meatl, which means it has 5% zinc and no more to be successful, with 95% bronze. You can obtain this from Thompson’s Enamel and use their unleaded enamels used for copper as long as you have no more than three firings.
History and Facts About Enamels
Art Enameling on Metals by H.H. Cunynghame 1906
Metals such as gold, silver, iron, copper and fine brass; copper with a small amount of tin, are capable of being enameled. But nickel, zinc, or common brass, which contains a mixture of copper and zinc are not capable of being enameled. Mr. Cunynghame, first speaks of the art of enameling is simply melting glass on to the surfaces of various substances capable of adhering to it and also capable of withstanding the heat necessary to melt the glass and cause it to flow. Mr. Cunynghame, speaks of the common technology of producing Crockery, with is clays consisting of silicate of aluminia and magnesia, and forming it into shapes and firing it. After this process it is know as biscuit ware, and is hard and porous. At this point glass ground to an impalpable powder is mixed with water and the vessel dipped into the glass slurry, dried and fired to the melting point of the glass. In this respect the glass is called “glaze.” Very similar to our enameling and as well as the commercial applications of enamels or glass on other foundations such as iron= stoves and refrigerators or bathtubs. And don’t forget the use of enamels on signage.
Glass consist of sand and an alkali such as soda or potash, fused together with the addition of ingredients to produce color. He states the peculiar value here of lead. It gives the glass the remarkable ability to adhere to and run over the item being enameled and prevents it from cracking. He state it makes the glass more elastic and enhances its’ ability to withstand extreme temperature changes. He also says that glass without lead is not suitable for enameling, as it will crack away from the metal. Of course today we have found a way to produce enamels without lead. The replacement for the major part is borax.
Glass is colored by melting it with the oxides of various metals. Oxide of tin makes it opaque white, iron gives it a sea green and yellow, cobalt a royal blue, and copper a turquoise blue. Manganese colors glass violet, silver and antimony yellow, and gold crimson. Also we have chromium, producing a fine shade of green; uranium, a fine yellow; and iridium, giving enamels the shades of steel gray and black.
Coefficient of thermal expansion is when the temperature of a substance changes. The energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds. As a result, solids typically expand in response to heating and contract on cooling. This dimensional response to temperature change is express by its coefficient of thermal expansion. This is where many get lost.
In enameling you just need to match the expansion of your metal and your enamels. I use a harder firing enamel as a flux = base layer in the technique of cloisonne, , still in the family of medium expansion enamels but slightly harder. Then continue with medium firing enamels just a bit softer. For the very simple reason, with repeated firings the base flux layer is harder to flow, and the medium temp enamels flow or fuse faster. If the base layer melted at the same temperature and time as the later layers it would be possible for your warm colors to get liquid enough to mingle down through the base flux and eventually touch the metal and burn. We are using medium firing enamels, they are for copper, sliver and gold metals, but a few are a little bit harder than others and these should be laid down first.
If you make test plates you will see this. Below I have a plate 1″ x 3″ and I put 15 color dots of washed enamel on the plate and fire it at 1425 degrees. Some dots are completely fused and some are still grainy. The grainy one is a harder firing enamel and takes more time to fuse.
Another point here to help in the technique of plique a jour, as well as in cloisonne, you do not want to put a harder firing enamel next to a softer firing enamel, again you will have cracking. When cooling the less expansion enamel right next to the high expansion enamel do not mingle, and separate= cracks.In this piece I made for Andre of Outkast, he wanted the cloison wires to be fine silver and different thicknesses. Which caused a lot of heat and of course with a pink nose against the fine silver cloison wires was trouble. But in my pallet of colors my pinks were not of the same firing hardness, once the cracking started, I had to remove them and test to get ones that were all the same to get the cracking to stop. And I am not talking about layering these colors I was gradating the colors next to each other. Things like this teach you but it would have been nicer to know ahead of the project.
When you get into plique a jour you will find it is also important to know your enamels melting points as in grouping or shading. When laying colors next to each other with no backing it is more obvious if the colors do not blend together. When the grains do not mingle and with out the back foundation as some expansion unity it is more likely to have cracking.
Color plates are very important. And yet so many choose not to do them. I know it takes time and you can get recommendations of colors from other artist, but if you have a direction in your work, by that I mean, a vision of your complete art form, and you want to get to that vision the practice of doing color plates can not only save you time and frustration but also end with the beautiful jewel you had visioned. As in rendering a water color of your visioned jewel can help you with your color choice, making a color plate to test how the colors work together can make you more successful in this medium.
This is a color plate,
There is a lot of information on this plate, see what you can find. No matter if you are working in the technique of Cloisonne, Plique a Jour, Champleve, or sifting on colors of enamel, you should know the properties of the products you are working with.
1. This is my pink color plate. Some artist have just a few colors and mix two, to get a color shade in between them. I prefer to have separate colors, one reason I have mixed colors together and came out with a speckled effect, so I have a choice to set them next to each other to work in a color family and be able to go from light to dark.
Also there are problems here. And if you were to mix some of these together you will have cracking.
2. First, I notice the 4th enamel dot did not flow at the same temperature and time as the rest of the enamel dots. This means the expansion rate is different in the two enamels. The one that is grainy has a higher expansion rate, than the ones that are smooth.
You can layer enamels of different expansion rates with the higher on the bottom but if you put them side by side in a cell or on any enamel piece you will have cracking. The odd thing is it may not crack today or even next month, it could be in two years. Enamelist like to use the terms soft and hard enamels. Hard enamels on the bottom and soft enamels on top. Enamels that are hard are used on the bottom as it takes longer for this enamel to fuse and flow smooth. This also gives you a hard base that will not become liquid at the same time as the second and third layers of enamels you use to create colors. What does this mean? If you like warm colors and we all know warm colors burn. This can help you prevent that. The reason they burn is they come in contact with the metal. So ideally you want to keep them away from the base metal. And with a hard base = flux or several layers of a hard flux your warm colors will not penetrated to the lower levels and touch the base metal. This way the in the next layers softer enamels will fuse and flow before the harder base enamel becomes liquid= no burning. I recommend Bovano #3 for fine silver as it is harder than other fluxes I have tested.
3. The 7th color dot has a bit of yellow in the base color. What would this mean to the enamelist? Enamels have colors bases of yellow, ash or blue. When you line up your colors this way you can easily see which are which. If a color you have chosen for your design has a yellow base, you would want to add it as you last color layer as it will also have a tendency to burn. Your enamels with a blue base or an ash base are safer. And yes you have yellows that have an ash base, or ones that are true yellow. = Test plates!
4. # 10 and #13 Are pinks with a blue base. These are less likely to burn that the yellow base ones, but will if allowed to come in contact with the metal. If you want a yellow pink just use the blue base ones first then the yellow.
These two images show problem with the soft enamel being used on the bottom and the harder enamel on top. When heated the soft enamel bubbles up and around the hard enamel.
Some thing you can do to enhance your work is to carve in the enamel. On this Nautilus Pendant I used white Askansas Stones to carve out the shape of the shell’s spiral.
Thank for the visit. I was not at the conference, but Merry-Lee Rae presented a lecture on cloisonne and used my images.
On carved enamels, yes I used a layer of flux and two layers of transparent red enamel. You can use a very fine diamond bit and arkansas stone bits. Afterward you should glass brush and or steam the piece to remove any trace of the stone and flash fire.
But as you know the layers are thin as transparent enamels need to be for clarity. And if you lay in the enamel in that small of a space it flows even. The chased flower petals had ridges and valleys. To enhance the visibility of this I carved in the top layer to follow this and expose the ridges more.
The Nautilus is also carved. This is posted in the topic Enamels, under Carving in Enamels. But this is a complete cloisonne piece, so the wires are at least .040″ high. And I actually over filled this, then carved the spiral of the shell into it.
Good luck, Patsy Croft