Separation Enamel - Old and New Variations
by Tom Ellis
from Volume 11, No. 2, April 1992
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     Separation enamel has been an accessory enameling product for many years.  Traditionally it has been placed alongside of techniques that some will label "hobby techniques" such as scrolling, the use of lumps and threads, and "happy accidents".  It has been considered a high fire technique with little control of the outcome.  Objects made from the separation technique have most often been limited to forms with sloped sides or bowls.  For many years, Thomas C. Thompson Co. sold lead bearing separation enamel.  If this product was not properly thinned with oil, a black residue would result after firing.  It also did not seem to work well on flat surfaces.  Several years ago, Ceramic Coating Company developed a lead free separation enamel.  This is now the separation enamel that Thompson Enamel carries.  The lead free separation enamel has several advantages over the lead bearing separation - the absence of lead, the availability of the product in dry powder, as well as oil base, no residue after firing, and the ability to work on flat surfaces.
     The physical principle that separation enamel is based on is viscosity (see Enamel Potpourri in this issue for more in-depth information).  When separation enamel is fired onto an enamel surface, a depression or indentation develops where the separation was applied.  When two or more parallel lines of separation are fired into a transparent enamel, the areas in between the lines become more intense in color and the indented areas less intense in color.  When parallel lines are fired onto 2 or 3 layers of enamel, trace amounts of each color layer become visible.  By varying elements to the process such as color choice, combining opaque and transparent layers, placement of enamels, placement of separation, firing times and temperature and enamel thickness, many different results are possible.  With experimentation and consideration of the above elements, separation enamel becomes very controllable and offers much potential as an enameling technique.

THE PROCESS
Counter Enamel Application
     Whatever form is decided upon, a substantial coat of enamel should be applied to the back side of the piece.  If several coats of enamel are planned for the front side, an equal amount of enamel should be applied to the back.  Thin coats of enamel are preferable.

Options on Layering Enamels
     Direct on Copper Transparent* - A simple and effective use of separation is to apply it to a transparent enamel that works well direct on copper, a single coat of a "direct on copper transparent", fired, then an application of separation enamel, fired until the transparent becomes clear.
     Transparent Clear - Transparent clear enamel (flux) used as a base can be covered with a coat of transparent enamel and then separated.  Another option is to apply a light colored opaque for the second coat, and then any transparent for the third coat before separating.
     Transparent Color - A transparent color can be substituted for the above use of a transparent clear with different results.
     Opaque - Opaque enamel can be used as a base with a transparent applied as a second coat, then separated.
     Stencil - The second coat application can be stenciled onto the base coat so that some areas of the base coat become part of the design.  Stenciling the second coat is one means of controlling the influence of the separated areas in relation to the overall composition of the work.  Use any transparent for the third coat application, covering the whole piece, then separating.
     Wet Inlay - One or more opaque enamel colors may be applied onto the base coat in the wet inlay method to develop a design or pattern leaving areas of the base coat exposed.  Again, use any transparent for the third coat application, covering the whole piece, then separating.  After each firing, always stone the edges.

Preparation of Separation Enamel
     Oil Base - Using a small spoon or knife, take out a suitable amount from the jar and apply onto a piece of glass.  Using oil from the jar, thin the enamel to a paintable consistency with a palette knife.  Mix thoroughly.
     Dry Powder - Klyr Fire or any gum and a small amount of water mixed with a palette knife on glass to a paintable consistency works well.  The dry powder can also be mixed with a variety of oils.

Application of Separation Enamel
     Screening Methods - Separation enamel is very finely ground so it is suitable for making a screening paste which could be used in a variety of screening methods.
     Sgrafitto - Separation can be applied over the whole surface of an area or piece and after drying, the design can be sgrafittoed in.
     Stencil - Gum can be applied to the final coat of fired enamel and then a stencil is adhered.  Dry separation powder can be sifted through a 150 mesh screen onto the stencil for unique effects.
     Painting Methods - By far, the most versatile means of controlling the outcome of the separation work.  The separation enamel is applied with a small brush.  The painted lines should not be any wider than 1/8".  When painting lines, the consistency of the application should be rich enough so that when dry, the lines are a consistent opaque ochre color.  Separ-ation is most effective when the painted lines of the design are at least 1/4" from one another, running parallel (or concentric circles, squares, etc.).  The idea is that when two parallel lines are fired, the enamel flow in between the lines is part of the excitement of separation.  Lines should not be spaced too far apart.  The lines should interplay with one another.  Figure 1, above, shows different separation line patterns that work effectively.
     If the stencil or wet inlay method of applying underlying enamel is used (as mentioned above under "Options for Layering Enamels") then the separation lines applied should somehow relate with or extend the underlying pattern or design of the stencil or wet packed areas.

Firing
     Separation enamels should be fired at 1450°F for 2½ to 3½ minutes, depending on size of piece (smaller pieces may take less time, larger pieces more time).  If working on steep sided forms, after firing the separation the enamel may tend to flow toward the bottom of the form.  This can be reversed by firing the piece upside down on the last firing.
     On flat pieces the surface of the enamel can actually be sculpted with separation enamel.  The separation should be fired at a slightly lower temperature, 1400° - 1450°F for 2-3 minutes.

Separation in Conjunction with other Enameling Techniques
     Separation can be used effectively when it is placed only in specific areas of a piece.  Using the stencil technique, some areas within the design could be separated giving a visual texture to those areas and leaving the other areas as solid color.  Gold or silver foil could be added to the solid colored areas for highlights.  Another approach is to use separation as a means to achieve a border around bowls, plates or wall pieces, with interiors using other enameling techniques.  Underglaze black can be used under any of the transparent bases used in separation to expand textural effects.

Additional Tips
     If the applied separation is too heavy or too much is applied in a given area, sometimes these areas will become dull or matte looking a few days later.  This can be corrected by applying another coat of transparent enamel over the area.
     On the other hand, if an insufficient amount is applied, or the underlying coats of enamel are applied too heavily, the separation effect will not be very apparent.  In this case, apply the separation again and refire.
     When using steep sided forms for separation, many times the back side will develop stilt marks.  After firing the separation enamel, stone down the stilt marks until smooth.  Also stone off any residue enamel on the stilt arms.  Apply another coat of counter enamel and refire upside down.
     Imagination and persistence are the keys to having fun and success with separation enamel.  Some combinations of color may work out sensationally, while others are disappointing.  If using opaque enamels, the light to medium colors work best.  Transparent colors fired over darker opaques tend to get lost.  A good test to figure out successful color combinations is to coat a square piece of copper with stripes of different colors,  then fire.  The second application is again stripes of different colors, but applied perpendicular to the first set of stripes.  All colors should be written down on paper as to their placement.  Separation is then applied to each color square.  After firing, many possible color combinations are apparent.
     Separation enamel can have a place outside of the "hobby" category. 

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     *Direct on copper transparents - There are many transparent lead free enamels that fire successfully direct on copper without using a clear base.  Some of my personal favorites are:  2210 ivory, 2115 Mars, 2170 VanDyke, 2220 Chartreuse, 2325 Gem, 2420 Sea, 2520 Aqua, 2530 Water, 2615 Periwinkle, 2625 Winter, 2650 Heron, 2680 Prussian, 2755 Concord, and 2820 Pink.