There are many interesting and diverse pottery decorating techniques involving the use of slips. Effects range from very linear to very textural and from very fluid to quite hard-edged.
Slip trailing is one of the most widely known and used methods of decorating with slip. Slip trailing delivers a stream of slip to damp or leather-hard clay through some type of dispenser.
This dispenser can be a large-bore syringe such as a baster or a bottle with a nozzle such as is used for condiments or glue. In either case, the dispenser's opening must be wide enough so that it won't easily clog -- the slip used consists of fairly fine particles.
After trailing slip over damp or leather-hard clay, slip trails can be modified by turning or shaking the piece of pottery or combing through. The effects achieved will greatly depend on the method of modifying the slip and also on how fluid the slip itself is. For example, the slip may take a drizzle-like shape, or contrasting and more liquid slips can be shaken for a very fluid effect as shown.
If you do use a very liquid slip, be aware that you will need to carefully control the piece's drying time. Slow drying and ensuring there is air flow all around each side of the piece will greatly lessen the possibility of warping or cracking.
Also known as feathering, this technique begins by applying bands of contrasting slip onto damp or leather-hard clay. If the bands are applying using slip trailing, the dispenser's end may be used to spread the slip slightly to produce a wider band that abuts with the band(s) next to it.
After the bands have been widened and are adjacent to and touching each other, a soft, flexible and sharply pointed tool is drawn through the slip to produce a chevron pattern. Tools used include finely pointed brushes, such as liners. It is likely that the traditional tool was the flexible end of a feather, hence the name.
Feather combing can take quite a bit of practice to master, but it does have very interesting potential.
Slip and Brush Decorations
When decorating pottery, slips can be applied to ware using brushes. This is best done when the clay is damp or leather-hard.
Brushing slip onto pots is one of the oldest methods of delivering slips to a pottery surface. The brushed decoration can range from very delicate lines done with fluid, fine-particle slip, to an overall layer of heavy slip applied with wide brushes.
One method of decorating pottery is to do slip paintings. Multiple colored slips can be applied to create pictures or designs on the damp or leather-hard clay surface.
Like traditional painting, slip painting is usually done with a brush because the slip can also be trailed or dabbed on with a sponge or the fingers.
Terra sigillata (or terra sig, as many potters call it) is an ancient technique of decorating pottery. It is most famous for being the slip decoration of choice by ancient Greek potters, as well as its use by Pueblo potters in the southwestern United States.
In the terra sigillata technique, no glaze is used at all. Instead, an ultra-fine slip is evenly applied to bone dry greenware and then burnished to a high gloss. After firing, the ware is usually burnished again.
Slips and Resists
Slips can be used with resists in order to decorate pottery. In this technique, slip is brushed onto damp or leather-hard clay after a resist of some form has been applied. The resist is placed in areas which are to remain slip-free.
Resists such as wax emulsions and hot wax repel the slip. Any slip that falls into those areas beads up and is easily wiped away. The resist will burn off during firing.
Paper resists and masking tape can also be used. These resists are more like what you may consider a stencil to be.
For paper resists, the paper can either be pressed onto damp clay, or it can be moistened slightly and applied to leather-hard clay. Once the paper or masking tape is applied to the clay, the slip is brushed on. The paper or masking tape is carefully lifted away once the slip has stiffened.
One of the really nice things about using resists and slip is that hard edges and intricate patterns can be achieved.
One way of decorating pottery is to use slip texturing. Although we usually think of slip as being fine-textured and of an even consistency, this doesn't have to be the case.
Slips can have inclusions added such as grog or sand. They can also simply include clumps of the same clay as the slip itself, rather like lumps left in mashed potatoes.
These inclusions and clumps can be used for decorative effects. Textured slips can be applied in small, specific areas. They can be dripped or trailed using a brush. (The large particles will clog nozzles or syringe tips.) Textured slips can also be applied across an entire pot, rather like applying sanded stucco to a wall. Or, you can mix and match to achieve your own vision.