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Liquid Enamel

How to...Liquid Enamel
An Ideal Technique for the Beginner and Novice: 
Using Lead-Free Enamel
by Tom Ellis
from Volume 6, Number 6, December 1987

Figure 1
     Many times we are asked here at the Thompson company - "What technique or project would be suitable for a beginning group that would be inexpensive, require little equipment or tools, would be fairly easy to set up, and would be safe for younger students?"  A process that seems to fit the requirements is the use of lead-free liquid enamel, the sgraffito technique, and lead-free transparent enamel.  
     As with most enameling projects, the student is challenged to create a design of his/her own inspiration, however, if this step of the project becomes a stumbling block for some students, it is easy enough for them to find a suitable image from magazines, photos, etc., that can be traced onto tracing paper, the same size as the metal, and then transferred to the dried liquid enamel using the pencil tracing technique1.  For those with active imaginations, this project is a good exercise in drawing and the use of color.  The subject matter of the image is not so defined or restricted as it can be in other enameling techniques such as cloisonne or champlevé.  The image can be loose and abstract or realistic with some degree of detail. 

SUPPLIES: 
     Metal:  Copper is generally used as it is readily available in many sizes and shapes, flat or formed, and is reasonable in cost.  Any size or shape is usable in this process, but sometimes it is advisable in a class of 8 students or more to limit the choices.  3" squares or 3" x 4" rectangles make a good "canvas" to learn the process.  Once the student has become familiar with the process, then he or she can use the process on a larger piece of copper, or a three-dimensional copper form.  
     Enamel:  Thompson's CE-3 Lead-free tweed counter enamel is recommended for the back of the piece unless a metal form is used that would require the back to be color related to the front such as a bowl.  If this is the case, use a suitable lead-free enamel.  
     For the front or design side of the piece, BC-l0l0 liquid opaque white, 533 white crackle, or BC-969A liquid transparent flux is used.  
     In step 8 of the process LF-302 flux is used to cover the oxide formed in the previous firing of step l.  
     For the final step of applying color to the design, if the BC-10l0 or the 533 white is used as a base enamel then lead-free transparents with expansion coefficients of 315 or less should be used.  Enamels with higher expansions tend to crack when fired over BC-10l0 or 533 white Expansion measurements for all Thompson Enamels are found in the Thompson Enamel Workbook.  All lead-free enamels work well over the BC-969A 

TOOLS AND EQUIPMENT: 
     1.  Any size furnace will work in this technique.  The furnace should be large enough to easily allow the enamel work to be moved in and out, although a hot plate furnace will work fine if the copper pieces are suitable in size. 
     2.  A wire grid and trivets suitable to the size of the furnace and the copper pieces, will be needed.  
     3.  A firing fork or a mason's trowel is needed to move the enamel, trivet and grid into and out of the furnace. 
     4.  A non-asbestos protective hot pad (PH-l in the Thompson catalog) or a square foot, ¼-½ inch thick piece of sheet steel or iron is needed to set the hot ware on as it comes out of the furnace. 
     5.  Heat resistant gloves are optional but may be used if the instructor feels they are needed as a safety precaution.  An approved dust respirator or mask may also be advisable as a safety precaution.  
     6.  A 2" diameter sifter is needed to apply the counter enamel to the back, and to dust a light coat of LF-302 on the front.  
     7.  A medium size bowl is needed to catch the runoff of the liquid enamel as it is poured onto the copper.  
     8.  A sharp wooden or plastic point is needed to draw the design into the dried liquid enamel.  (Metal points tend to scratch the copper leaving undesirable scratch marks that show through the enamel.) 
     9.  Scalex - a clay slip used to absorb the firescale that forms on exposed copper during the firing process.  A medium size brush is needed to apply the Scalex. 
     10.  Sparex No 2 or a suitable pickle is optional if the BC-1070 is used as a base.  Pickling the metal before counter enameling and then again before the liquid enamel is applied is not absolutely necessary with the BC-1070 or 533 The counter enamel and liquid white will both adhere to an oxidized surface providing all loose scale is removed.  The metal would need to be pickled before BC-969A flux is applied if a clear transparent blemish-free base coat is de- sired The flux would adhere to an oxidized surface but the oxide will fire as rust colored areas The real advantage to pickling the metal whenever it has oxidized is that it eliminates any firescale or oxide which could potentially contaminate the enamels around the work area.  
     Note:  A completely safe alternative pickle is vinegar and salt.  Take a cloth dampened with vinegar, daub into common salt and scour the metal surface Vinegar contains 4 to 8% acetic acid which reacts with salt forming a week hydrochloric acid.  This procedure is effective for small ware.  Much of its effectiveness is due to the mechanical action of scrubbing.  If considerable pickling is to be done in this manner, it is best to wear rubber gloves to prevent finger stains.  Metal shapes may be submerged in a solution of vinegar and salt.  Use about 45 grams (16 ounces) of salt to one cup (8 fluid ounces) of vinegar.  If necessary, the instructor can perform the pickling procedure for the whole class.  A Pyrex dish or 2" deep plastic tray is needed to hold the pickle.  
     11.  A pair of copper, wooden, or plastic tongs will be needed to remove enamel piece from the pickle A water source and paper towels are also needed.  
     12.  An alundum stone or file, and 000 steel wool are needed to clean up the edges. 
     13.  Klyr-fire may be needed as an adhesive 

PRECAUTIONS: 
     Students should be made aware of a few simple safety precautions. 
     1.  An approved dust respirator or mask should be mandatory for minors when scribing into the dried enamel and when the enamel is being sifted.  This can be optional for adults.  
     2.  Food or drinks should not be allowed around the enamel area.
     3.  Safety goggles and rubber gloves should be worn when using the Sparex No 2.  The pickle (Sparex No 2 or other suitable pickle) should be placed in a well ventilated area.  
     4.  Care should be taken when firing the ware.  Trivets or grids should never be picked up without first checking to see if they are hot.  (An Aloe plant is wise to keep on hand in the event that someone accidentally gets burned.) 
     5.  Good housekeeping around the work area is always advisable.  Old catalogs, telephone books or computer paper work well as "catch paper".  When sifting enamel onto the work, the excess enamel falls onto the paper.  If the enamel remains clean and pure of any other enamel colors, then it can be returned to the original container.  If it is contaminated by dirt or other enamel, then simply fold the paper in half and discard. 

THE PROCESS: 
Figure 2     Two decisions need to be made at the beginning.  First, the size and shape of the copper need to be determined.  Next the choice between the liquid white or the liquid flux is decided.  There is not a great difference between the two, but generally speaking the transparents over white tend to be a little brighter, and some yellow transparents tend to take on a greenish cast.  To get a more accurate idea of how they compare, make a small test strip, coating one vertical half with white, the other vertical half with flux; fire; then sift horizontally strips of each transparent color to be used in the enamel project, and fire.  
     With the above decisions made, and all the tools and equipment gathered, we are ready to begin the process. 
Figure 3     1.  The copper piece is degreased in the furnace for 20-30 seconds.  When cool it is placed into the Sparex No 2, back side up, for about 5 minutes.  Remove from Sparex and rinse with water.  Dry with paper towels being careful not to touch the back side of the piece with your fingers (oil from the skin may cause a smudge on the cleaned surface).  Pickling may be omitted with fair results if Sparex No 2 or other pickles cannot be used for safety reasons, if so, brush off any loose oxide after degreasing and go to step 2. 
     2.  Next coat the front side of the piece with Scalex, again being careful not to touch the cleaned back side with your fingers.  Allow the Scalex to dry.  By applying Scalex to the front side, it will make removal of oxide from the front side much easier after the firing of the next step. 
Figure 4     3.  Counter enamel is now sifted onto the clean backside of the piece.  If the copper is flat, the enamel can be sifted on dry.  If it is a three-dimensional form, then the copper surface should be sprayed or brushed with a solution of klyr-fire and water (one part klyr-fire to 3-5 parts water) and then the counter enamel is sifted on.  If klyr-fire has been used, allow to dry and then fire the piece for 2 minutes at 1450°F.  Allow to cool.  Rinse off Scalex flakes. 
     4.  If Sparex No 2 is being used, place the piece into the solution with the front side facing up.  Remove piece after 5 minutes and rinse with water, then dry with paper towel.  If a pickle is used, the edges need not be filed after the firing of the counter enamel, but after all further firings, the edges should be cleaned of firescale with a file or an alundum stone.  Otherwise firescale will continually pop off the edges, and if the piece with uncleaned edges is placed near the enamels, it may potentially contaminate them.  
Figure 5     5.  Shake the liquid enamel up quite well, then pour on a small amount onto the front side and roil it around until the front is completely covered.  Drain excess enamel until only a thin coating is left.  If ample time is available the piece will dry adequately in a few hours, however, there are several ways to speed up the drying time to only about 15 minutes.  The piece can be heated to about 300-350°F.  Higher temperatures may cause the water in the enamel to boil, bringing about undesired results.  A heat lamp may be too hot for this purpose.  Instead, a 100 or 150 watt bulb directed towards the piece should work sufficiently.  The top of an enameling furnace works well as a heat source for drying ware, although the top of a hot-plate furnace is most likely too hot.  Another way is to heat up a grid and trivet in the furnace, then set the hot grid and trivet onto a protective hot pad.  The ware to be dried is then placed on top of the hot trivet.  It should dry sufficiently in about 15 minutes.  It is very important that the coating is thin and the enamel is completely dry before firing, otherwise the enamel may crackle during firing.  
     An alternative to pouring the liquid enamel is to spray the liquid enamel onto the piece.  Either a Preval Aerosol spray kit or a spray apparatus hooked up to an air compressor would be needed to spray the liquid enamel.  The very thinnest coat possible can be accomplished by spraying.  This would eliminate any crackling of the white and would prevent cloudiness of the flux (cloudiness due to a thick flux coating).  In order to attain a fine spray, water may be added to or removed from the liquid enamel.  It may require a little experimentation to find the right consistency. 
Figure 6     6.  At this point. a design may be transferred onto the dry enamel via the pencil tracing technique or the design may be sgraffitoed or scribed into the dry enamel freehand, with the sharp pointed wooden or plastic tool.  It is advisable to have the student wear an approved dust respirator or mask during this step.  As the design is scribed, the excess enamel is blown off of the piece and away from other students.  
     7.  Fire the piece at 1400°F for 2 minutes.  
     8.  When cool, the piece should be rinsed off with water and dried.  Sift a very light coat of LF-302 to lightly cover the oxide formed around the scribed lines in the previous firing.  Use a little klyr-fire if the piece is three-dimensional, to hold the LF-302 in place.  Allow to dry. 
     9.  Fire the piece at 1450°F for 2 minutes. 
     10.  The piece is now ready for the application of transparent enamel colors.  This can be done in several different ways.  Figure 7Transparent enamels can be sifted on dry, in specific areas with a small sifter, then the boundaries of these specific areas may be "cleaned up" with a small brush.  The enamel could be mixed with water and wet packed into place via a spreader and spatula; or full strength klyr-fire can be painted onto the exact areas that are to be colored and then the transparent enamel color can be sifted over the klyr-fire.  The piece is picked up and turned over, gently tapping the edge and the excess enamel will fall off leaving enamel only over the areas painted with klyr-fire.  Another possibility is to cover the entire surface with a light to medium-light transparent and fire.  Then, medium to dark transparents can be applied as a border around the piece or to shade certain areas similar to the way the light areas are painted first in a water color with darker colors applied later.  For any of these methods it may take two or three applications and firings of the transparent color to make them dark and even enough. 
     11.  The final step is to clean the edges of firescale and excess enamel with an alundum stone or a suitable file.  The edges are polished with 000 steel wool.  Note: Steel wool should be kept well away from the area where the enamels are being used; this prevents contamination of the enamels. 

  1. If the design is traced from a magazine or photo, there is the problem of the traced image fitting the size of the copper blank or form.  An easy way around this is to lay the copper blank onto a white sheet of paper and trace around the edge.  Cut out along the traced lines leaving a hole in the paper the exact size of the copper piece you plan to work on.  The paper now becomes a "window" which can be laid over a photograph and moved around until the image seems to work well proportionally to the size of the opening.  The "window" is taped down securely to the photograph and then tracing paper can be taped over the "window" and the lines of the image are traced on to the tracing paper with a pencil. After the image has been traced, the tracing paper is placed, with the traced side down, onto the dried enamel surface.  The backside of the tracing is gently rubbed so that the traced image is partially imprinted onto the dried enamel.  This leaves enough of a line to scribe from. 

 

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