Take a deep dive into the technique of Dendritic slip decoration. Learn the history and science behind this unique process, then discover what materials you can use to try it on your own. 

Defining the Terms 

Bleed Edge: A blurring of color on the edge of the dendritic slip pattern. 

Clay Body Formula: Composed of clays, feldspars, talc, frits, silica, or other ceramic materials. 

Dendritic Slip: Caused by the reaction between the wet underlying slip and the wet covering slip. A wet-to-wet slip application is required for the pattern to develop due to the unstable tension between the slips. 

Marangoni Effect: A disturbance of the liquid-liquid interface, due to interfacial tension, has on mass transfer in a liquid-liquid extraction system. 

Wet Slip: Composed of water, clay(s), and/or other ceramic materials that can be applied to wet or leather-hard ware, resulting in the covering surface fitting the underlying clay body. 

Mocha Ware 

Dendritic slip decoration—whose name is derived from the Greek word for tree—is a delicate fine-lined slip pattern that looks very much like a complex series of tree branches or veins of seaweed. Interestingly, this pattern also develops in nature such as lighting forking when it hits the ground or rivers branching into tributaries. 

1 Wisconsin Pottery’s platter with dendritic slip pattern, 9 in. (23 cm) in diameter, fired in oxidation to cone 04.

Mocha ware, banded creamware, and dipped ware are all terms used at various times to describe this type of pottery. One origin of the name Mocha ware is from the Yemeni port city of Mukha. The city itself was called Mocha by the English-speaking world in the 18th and 19th centuries.1 Another derivation of the name comes from mocha stone, a quartz with moss-like patterns found in Arabia, which was imported to London in the last half of the 18th century. In the past, the generic term mocha ware was also used to indicate an extensive array of colored horizontal slip designs ranging from marbling (different color slips mixed together on the clay surface) to precise checkered patterns of slip trailing on pots. Some ware had a decorative textured design impressed in the moist clay or variation of colored slips applied in exact patterns on the pot’s surface.2 

The Beginning of Dendritic Slipware 

Mocha ware also includes the subcategory of dendritic slipware. However, today, especially in Britain, the term mocha ware refers to pottery made using the dendritic slip technique. While this distinction was not made in the past, the terminology reflects current usage. The distinctive mocha pattern was an innovative decoration on simple-shaped utilitarian forms such as cups, teapots, salt containers, jugs, bowls, and plates. In its initial period of production, it was the least expensive factory-made decorated pottery available for common use. The most popular items produced were mugs and tankards. Oddly, flat pieces such as plates, platters, or serving trays do not occur when investigating mocha ware. The pottery was used daily in English kitchens and taverns and was not regarded as high quality. Each piece was thrown on a potter’s wheel, after which it was lathe-turned, producing refined utilitarian red or white earthenware whose principal decoration was manipulated slip. 

Slip Application and Pattern 

There are two pattern variations of dendritic slip. In the first, the most recognizable, called seaweed, a brush was dipped into the “mocha tea,” which was made by boiling tobacco into a thick mud, thinning it with water, and adding a metallic coloring oxide. It was then loaded onto a brush and barely touched to the wet slip causing the distinctive pattern as the pot was spun on the wheel. The technique caused a noticeable horizontal spine of dark color on the lighter-colored slip. The distinctive darker tree-like branches radiate from where the brush was dragged through the slip. Gravity and chance play a somewhat accidental factor in the dispersal of the pattern with many tree-like variations possible. The overall glazing techniques guaranteed that no two patterns were exactly alike. There was an aesthetic contradiction between the straight conservative pottery forms of bowls and cups and the random tree-like patterns created by the dendritic slip application. 

2 Applying black dendritic slip to wet white slip. 3 Black dendritic tree slip pattern drying on an oval platter.

The second and most identifiable type of dendritic pattern was formed when the pot was held upside down and the mocha-tea-filled brush touched to the underlying wet slip causing the tea to run down and spread the distinctive branch pattern.3 In nature the tree pattern is present in moss agate gemstones. The same alkali/ acid reactions are at work in conjunction with iron and manganese metallic oxides found in many dendritic slip patterns.4 Additionally, from approximately 1790 to 1810, a combination of slip marbling (different color slips in the wet state are dragged through each other causing a marbled pattern on the ware) and dendritic slip tree patterns appear on the same pottery. This type of pottery was believed to be a minor subcategory in the production run.5 

4 Tree pattern on cup, fired in oxidation to cone 04. 5 Close-up view of a black tree pattern. Note the dense to light migration of black slip formed during the application process.

Why Dendritic Slip Works 

The unique dendritic slip pattern is caused by a reaction between the wet underlying clay slip and the overlying wet application of dendritic slip. The instability where the two slips meet produces a surface tension gradient creating the tree pattern. This impressive dynamic reaction takes place within seconds. The contact line between the alkaline clay slip with a higher pH and the acidic dendritic slip with a lower pH becomes unstable as the surface tension of the dendritic slip is less than the underlying slip.6 The immiscibility of both liquids yields the distinctive tree or branch-like pattern. This reaction is also known as the Marangoni effect.7 Another way of stating the effect is a mass transfer along an interface between two fluids due to surface tension gradient. 

The reaction is further enhanced when using a slip with a high clay content (alkaline) and a dendritic slip containing high levels of acidic materials such as tobacco, stale urine, hop extract, boiled leaves, lemon juice, coffee, apple cider vinegar, or any acidic material. While the dendritic slip technique has traditionally been employed at low earthenware temperatures, it can also work at the higher stoneware temperature ranges. 

In the past, one variation used chewed tobacco and urine, which formed the acidic component of the dendritic slip. The brown, blue, and green colors were produced by adding manganese dioxide, ground iron scale, cobalt oxide, or chrome oxide.8 Current research shows that the tree-like patterns can be colored by the use of the carbonate form of metallic coloring oxides. For example, cobalt carbonate is less dense and has a smaller particle size than cobalt oxide. Cobalt carbonate, having a greater surface area and lighter density, allows for an enhanced reaction in the dendritic slip as opposed to cobalt oxide, which is denser and does not remain in suspension.9 One noted exception is where red iron oxide is used as a colorant in the mocha tea. 

Mixing and Applying Dendritic Slip 

The dendritic slip technique can be applied to any clay body, fired at any temperature range, and fired in any kiln atmosphere. However, three main elements should be in place to ensure optimum results. 

  • A reliable clay body formula that fits the base slip and dendritic slip in the drying, bisque firing, and glaze firing stages. 
  • A base wet slip formula that fires to a contrasting color with the overlying dendritic slip. 
  • A suitable, acidic dendritic slip formula that will react with the underlying wet slip and be compatible with a covering glaze. 

Clay, Body, Glaze, and Slip Formulas 1

Clay, Body, Glaze, and Slip Formulas 3

Clay, Body, Glaze, and Slip Formulas 2

Clay, Body, Glaze, and Slip Formulas 4

6 Wisconsin Pottery’s black dendritic tree pattern on cup with handle, 4 in. (10 cm) in height. Photo: Courtesy of Wisconsin Pottery.

Applying Dendritic Slip 

After the pot is thrown, handbuilt, or otherwise formed, apply the base slip to the leather-hard clay surface as soon as possible to ensure a stronger bond between the slip and clay body. While the base slip is still wet, immediately dip a soft bristle brush in the dendritic slip mixture (dendritic slip settles very fast, so constantly stir it) and fill the brush with a small amount of the watercolor consistency dendritic slip. Then, barely touch the surface of the wet base slip with the brush. The dendritic slip will flow off the brush onto the base slip, leaving a pattern. A tree-like tentacle decoration can be developed by holding the pot vertically. Concentric ring patterns can be obtained by applying dendritic slip to the horizontal pot surfaces. It is important to note that the wetter the base slip, the greater the growth of the dendritic pattern. Timing is critical. If the base slip is dry when the dendritic slip is applied, the pattern will not develop. The reactive qualities of the dendritic slip can dissipate over time in storage. Always test both base slip and dendritic slip so they can interact successfully during the application process. 

After the application of base slip and dendritic slip, let the pots dry thoroughly, after which they are ready for bisque firing. 

7 Wisconsin Pottery’s jug with yellow background slip, brown dendritic pattern, and random green copper oxide pattern, 9½ in. (24 cm) in height, fired in oxidation to cone 04. Photo: Courtesy of Wisconsin Pottery.

Glaze Firing 

A transparent glaze application will reveal the colors of the base and dendritic slip pattern. The glaze can be dipped, brushed, or sprayed on the bisqueware. It is also possible to once fire greenware if the clay body, base slip, and dendritic slip fit compatibly with the covering glaze. Longer firing times are required than comparable bisque firing due to the clay body’s slow release of organic material and mechanical and chemical water in the first stages of the firing.10 

When choosing a covering glaze, it is important to test for transparency and stability in the firing process. Some glazes can run or move on vertical surfaces during the firing resulting in a bleed edge to the fine-lined dendritic slip pattern. 

the author Jeff Zamek obtained BFA/MFA degrees in ceramics from Alfred University, College of Ceramics, New York. In 1980 he started Ceramics Consulting Services, a ceramics-consulting firm developing clay body and glaze formulas for ceramics supply companies throughout the US. His books, The Potter’s Studio Clay & Glaze Handbook, What Every Potter Should Know, Safety in the Ceramics Studio, and The Potters Health & Safety Questionnaire are available from Jeff Zamek/Ceramics Consulting Services. For technical information, visit www.jeffzamek.com

  1. A definition supplied by Jonathan Rickard in his book, “Mocha and Related Dipped Wares,” 1770-1939 Published by University Press of New England. 
  2. Cited in an article by Jonathan Rickard, “Slip Decorated Refined Earthenware” p. 183 Van Nostrand Reinhold Pub. 
  3. Rickard, Jonathan, “Mocha and Related Dipped Wares,” 1770-1939 published by University Press of New England pp. 48-49. 
  4. Hopper Robin, Ceramics Monthly, April 2008, Answer Section page 16. 
  5. Rickard, Jonathan, “Mocha and Related Dipped Ware,“ 1770-1939 published by University Press of New England p 51. 
  6. The Observer’s Book of Pottery & Porcelain, by Mary & Geoffrey Payton, P. 114 Frederick Warne & Co. Ltd. Pub. 
  7. Morris, Stephen, www.physics.utoronto.ca/~smorris/edl/mohaware/mochaware.html. 
  8. Cited in an article by Jonathan Rickard, “Slip Decorated Refined Earthenware” p. 187, The Magazine Antiques, Aug. 1993. 
  9. Hopper Robin, Ceramics Monthly, April 2008, Answer Section page 16. 
  10. Zamek, Jeff, What Every Potter Should Know. Iola, WI: Krause Publications, 1999 pp 179-180. 
  11. Zamek, Jeff, What Every Potter Should Know. Iola, WI: Krause Publications, 1999 pp 178-182. 

Sources: 

Mocha and related dipped wares, 1770-1939 by Jonathan Rickard, Published by University Press of New England 2006. 
Robin Hopper has an excellent video demonstrating the mocha diffusion technique at; ceramicartsdaily.org/pottery-making-techniques/ceramic-decorating-techniques/mocha-diffusion/?floater=99. 
Catherine Riedel, House & Garden Magazine, Jan/Feb. 2009. 

Acknowledgements: 

Wisconsin Pottery, 1082 Park Avenue, Columbus, WI 53925, 1 800-669-5196, www.wisconsinpottery.com, supplied images of dendritic pottery. 
Frances Gubler, Collections Management Fellow, and Leslie Wright, Public Relations and Marketing Director, supplied images of Pearlware from the Shelburne Museum, www.shelburnemuseum.org
Richard Lehman, Professor & Chair, Department of Materials & Science Engineering, Rutgers University, New Jersey, supplied technical information on lead glazes. 
Jim Fineman, professional potter and technical editor.