A question came up today about hard, medium, and low firing enamels.
Hard firing enamels are fired at a higher temperature as in the 1500’s degree range or longer in the kiln.
Medium firing enamels I think of using in 1400’s degree range, or at higher temp as 1500 degrees, but less time.
Low firing enamels maybe fired in the 1300’s or even in the 1400’s with less time.
The purpose of all this is two things expansion of the metal being used and your technique being used.
Start with copper as it is used most commonly in enamels.
Copper oxidizes the fastest of the metals we use in enameling. We balance this by using medium firing enamels so they melt or fuse before the copper has time to oxide. If it oxides the enamel is likely to flake off or just discolor.
Many enameling on copper use the oxidation to get some beautiful colors.
You can fire at a higher temperature so it fuses quickly not allowing the copper to oxidize. Another way to balance this is to use finer grit of enamel. The finer grit will fuse quicker than a larger grit of enamel without allowing oxygen to get to the copper. This allows the enamellist to achieve that beautiful gold or stunning golden orange copper color.
It is best to know the fusing points of all your enamels so you know which ones to apply as a base or flux. Your base coat of enamel or known as flux, should be the hardest enamel you are applying to your base metal so you do not have these problems.
Above the flux was a lower firing enamel than the top coats. So as the top layers melted the flux rose up and the top layer of enamel sank down.
2) Same here,
The flux coat of enamel was not hard enough to prevent the following layers of enamel from touching the sliver. And the brownish color of enamel is just burnt.
In cloisonné we never want our warm colors to touch the silver. It causes burning. Silver is going to hold heat longer than copper so we use a hard firing base. And in some incidences we will use several layers of the hard firing flux before layering in our warm colors to be very sure the red never touches the silver base.
A comment to address
“I’m torch-firing, I always have my work in my sight so I just watch for signs of melting, which happens very fast. I’ve had “pull through” with Titanium White. Titanium White really reacts nicely with copper and you can get some really lovely, but unpredictable, effects. With a little overfiring the enamel turns a beautiful rust color and in spots will be green.”
Yes these effects can be used to your advantage, this is the oxidation of the copper coming through. And in torch firing I realize you are not going by temperature and have the advantage of seeing all that is happening.
Enameling on copper, as in painting enamel in this piece,
It is necessary to use a hard firing flux as it will be fired many times and I do not want the painting to disappear into the base coat of flux. Also in repeated firings the copper can still oxidize through the enamel and show a color change after many firings. As I paint in my image I need the painting enamel to adhere to the base coat of flux by firing the piece, then I can continue layering my painting with enamel colors (soft firing enamel)that fire at a lower temperature or less time. The domed metal add strength or less expansion. So it can handle a harder firing enamel without so much expansion or movement in the enamel. If the base coat was a lower firing temperature it would become soft enough in firing the image would distort as the enamel base or flux would move before the image enamels fuse. Painting enamels are a soft or low firing enamel= as they are ground to a face powder grit.
A color plate is a very good answer to help you know which is which when you are not sure.
The enamel dot fourth from the left is still grainy after all the rest are fused.
This color plate shows the top row, second from the right, as becoming liquid so much faster than all the other enamels it is completely flat.
If you have three enamel on a plate, one hard firing, one medium firing, one low firing and fire the plate once you will see they melt at different speeds.
If you want to use them all in one project just remember the hard is on the bottom then the medium and then the soft or low firing enamel. This is also why you can use unleaded with leaded enamels as long as you put the unleaded on the bottom as it is a high fire enamel.
A couple of things tiny bubbles in enamels can be from,
First the addition of Klye-fire. I do my best not to use this but I realize in some designs we need it. The last time I used Klyre-fire, a mixture of 1-5 parts distilled water was best. It helps on a 3d surface but I could still see a few tiny bubbles. Klyre-Fire is very helpful on plique a jour. But you do see time bubbles.
Second way you can get those frustrating tiny Bubbles in enamels can be from sterling silver that has not been depleted properly. The more you fire the worse they get.*(
And last that I have seen, specks that usually come from old or deteriorating enamels. When you wash them you see tiny white specks in the container. On your first few firing you will see some are white in your enamel, then continue firing some look like beige-brown goo, and sometimes they turn into bubbles.
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.
Here are comparisons of fluxes available for fine silver to enamelist. See in the test plate below the 5 fluxes I have tested to determine which is a harder firing flux.
Left to right Ninomiya 3, Nihon Shippo G-110, Old Thompson 757, and Soyer #3. I fired at 1400 for 1 min. All the fluxes except Soyer #3 fused. In the second Image you will see after another firing at 1400 degrees for 2 min the Soyer fused also.
You might ask why is this so important? Working with reds is why. If you have a low firing flux the red enamel is very likely to reach with the silver and turn the color od mud.
The only time I use any flux other than Soyer #3 is if I need a low fire flux, and that is only in Plique a Jour.
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 metal , 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.