Enameling

More About Lead Free Enamel
by Tom Ellis
Volume 10, Number 1, February 1991

     Many enamelers who have 'mastered' the use of lead bearing enamel and who may have considerable lead bearing stock on hand have expressed apprehension in making a complete switch to lead free enamel.  First, I would like to assure everyone that in my own experience I have found this transition completely feasible in all uses of enamel, many times with pleasantly surprising unexpected results.  The following information is provided with the intent of making this transition more understandable.

     The first ten years of my enameling experience exclusively involved the use of Thompson's lead bearing product line.  I was not aware that a lead free product line was available.  After using the lead bearing product line for a few years I began to develop a color vocabulary which consisted of Thompson's lead bearing numbers.  I became familiar with certain qualities that one enamel may have compared with another.  I also developed a working knowledge of which enamel colors worked best in combinations or juxtaposed.  To learn this color vocabulary took time.  This is probably the most difficult part of learning to make the switch from lead bearing to lead free.  Familiarization is the key to a lead free color vocabulary.

     Making your own fired color board is one of the best ways to familiarize yourself with lead free enamels.  The color board, once made, is an invaluable tool when deciding which colors to use.  To get the full range of possible colors, we suggest firing transparents over clear on copper, gilding metal, silver plated steel, direct on copper, and transparent pinks, reds and oranges over gold foil.  Opaques can be fired over copper.

     Many enamelists have developed set methods or routines of using enamels to obtain a desired result.  When attempting to switch from lead bearing to lead free, most often a simple substitution will bring about the desired result.  However, sometimes problems may arise if the only change that has been made is to substitute a lead free color for the 'old time favorite' lead bearing color.  In these situations the set method or routine may have to be looked at and altered.  For example, if an enameler had previously been used to obtaining a specific quality of lead bearing transparent red fired over flux, and did not find the lead free substitution suitable, then altering the method may be the answer; in this case using gold foil under the transparent red instead of clear.

     Many enamelers create problems for themselves because they don't consider the 'complete picture' when they set out to create an enameled work of art.  Too often, esthetic considerations are the primary and sometimes the only considerations made.  Bill Helwig wrote an article in the Vol. 3, No. 4, August 1984 issue of Glass on Metal, found on pages 50 & 51, which lists in detail all the things that should be considered when enameling.  Most often when Thompson customers call when an enameling problem, involving lead free enamel or lead bearing, the problem can be pinpointed to some variable on the list.

     This list, however, only labels the areas of consideration.  The nine volumes of Glass on Metal (especially the first four volumes) give in depth information on the physical properties involved in the process of enameling, whether it be lead free or lead bearing enamel. 

ADVANTAGES OF LEAD FREE ENAMEL

  • High Acid Resistance - As well as being more resistant to attacks from weather elements, high acid resistance allows art or commercial pieces with exposed metal areas to be submersed into acid for short time sequences without causing the enamel surface to become matte or dulled.

  • There is about a 25% reduction of weight in lead free enamels compared with lead bearing enamels.  (You get more enamel for your money per pound.)

  • Lead free enamel has a slightly 'scratch' harder surface than lead bearing enamel.

  • Lead free enamel has identical refractory appearance compared with lead bearing enamel.

  • Lead free enamel has an expansion range that is compatible with silver as well as copper.

  • The obvious health advantage of enamel without lead.

  • Lead free transparents do not require an undercoat of clear enamel as frequently as lead bearing do.

  • Lead free enamels are compatible with lead bearing enamels.

  • Most any technique that is employed with lead bearing enamel may be used with lead free enamel.

  • Lead free enamels do not require a 'high fire' to improve richness or clarity.

  • There is more continuity of color gradations from light to dark among the lead free opaque color pallet.

  • Lead free enamel costs less.

USING LEAD FREE AND LEAD BEARING ENAMEL ON THE SAME PIECE

     Many people have inquired as to how lead bearing and lead free enamel can be used on the same piece.  There are many possible ways to do this.  The main thing to remember is that lead bearing enamels should be applied ON TOP of lead free enamel.  Lead free transparent clears 2010, 2020, 2030 and 2040 or lead free opaque whites 1010, 1020, 1030, 1040 and 1045 can be used as base coats under lead bearing transparents or opaques.  Transparent colors such as 2110 Ivory Beige, 2325 Gem, 2520 Aqua, 2915 Oil Gray or 2680 Prussian Blue are among several lead free enamels which work well when fired directly on copper.  These can be used individually or in combination as a background color and then lead bearing opaques or transparents can be fired on top.

     Another way they can be used together is to wet pack them side by side or stencil them side by side.  Of course, in the cloisonné technique, individual cells can be packed with one or the other, in the same piece.  Again, if lead free is applied underneath, lead bearing enamel could be fired on top (after firing the lead free) within the same cloisonné cell.

     Certainly, lead bearing can be applied to one side of a form and lead free on the other side.

     Now, to break the rule implied above, we know of several enamelists who intentionally fire lead free on top of lead bearing.  This results in a textural surface which may add interest to a composition.

METAL PREPARATION & FIRING TRANSPARENT CLEARS

     When firing transparent clears and colors direct on metal, it is important that the metal is properly prepared for enameling.  For detailed information on metal preparation, see Vol. 1, No. 1, issue of Glass on Metal.  If you are using a mild acid such as Sparex #2 or vinegar and salt, it is advisable to glass brush the surface before applying enamel.

     When firing lead free transparent clears direct on copper, the firing must be sufficient for the enamel to absorb the copper oxide.  This may take two to three firings at 1450°F for 2 minutes.  The edges of the piece should be cleaned with a file or alundum stone after each firing.  This firing process is also necessary when firing transparent colors direct on copper.

LAYERING TRANSPARENT LEAD FREE ENAMELS

     The lead free transparent pallet can be expanded by layering one color on top of another.  For instance, to obtain variations of olive colors, transparent greens such as 2335 Peacock, 2340 Glass, or 2350 Grass are fired first.  Then by applying a second layer (on top of the green) of 2210 Egg or 2215 Soft and firing, an olive transparent color is obtained.  Another combination could be firing 2910 Elan Gray first, and then layering one of the transparent blues on top, resulting in a blue-gray transparent.

     Another way to expand the transparent pallet is to physically mix two transparent colors.  Any proportion of two colors can be run through a sieve a number of times and used as is (this may result in a spotted texture of color) or the two colors can be mixed by placing them on a sheet of paper and lifting up and rolling over opposite corners of the paper until the dry enamel is uniformly mixed.  For a purer color the mixture can be fired on mica or Thompson's furnace floor blanket and then re-ground with a mortar and pestle.  If using mica, any residue mica should be ground off the glass frit with an alundum stone before grinding in a mortar and pestle.  If using the floor blanket, a damp cloth will remove residue fibers on the bottom of the glass frit.

PHYSICAL PROPERTIES

     1010 opaque white is the most suitable white to use as an undercoat.  1020 opaque white is a titanium white.  It has great coverage ability to stay opaque.  1030 and 1040 are whites with medium opacity and work very well in the grisaille technique.

     1850, 1860, 1870, 1880 and 1890 are cadmium selenium colors, and will darken with prolonged firing.

     2880, 2850, 2840, 2210, and 2215 are cadmium selenium colors.  They chemically react with copper and silver and frequently turn opaque.  They will remain transparent on tombac, silver and gold for a limited number of firings.  They will darken with prolonged firings.  They are best used over another enamel.

     2825 and 2810 are gold bearing colors which will react with copper and frequently turn opaque.  They are best used over another enamel.

     2820, 2810 and 2830 are gold bearing colors which will require special firing for transparency if fired direct on copper.  First firing - 1450°F to 1500°F for two minutes.  If necessary, increase time, not temperature.  2820 is the best one to fire direct on copper.

     1050 matte enamel fires as a normal opaque.  It glosses on the first firing and will matte on subsequent firings.  It may require a longer firing time depending on the size of the piece.   

 

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