What's special about #6 Tile slip?

[Pyewackette]

I wanted to slip coat a piece the other day and someone pointed this huge bucket out as "white slip".

 

Turns out there is another "white slip" that is "regular slip" and looks entirely different.

 

How is #6 tile slip different from "regular" slip? What little I've been able to find on the interwebs mentions it in reference to salt firing, which I am not doing. I also found mention somewhere that it "tends to craze" which the writer seemed to consider desirable in salt firing.

 

The slip in the studio (it's a community studio) is very thick. Asking the studio coordinator about it is not an option as that person has been impatient with minor questions in the past.

 

I'm just wondering what is special about it that would lead to having it's own 5 gallon bucket in with the glazes instead of a little 2 gallon bucket over wherever they are keeping the slips, and how that may affect the 2 pieces I've already slip coated with it. For instance, am I going to need to use a cookie with those pieces? (I wouldn't think so, from the recipes I've seen for it, but better safe than sorry!)

[Benhim]

Tile 6 is a domestically mined kaolin used in many recipes here in the United States. White slip could mean anything, but a community studio I used to work in made a white slip from the scrap from several potters that used B-mix. This is called a white clay body slip and was thick in the bucket to be applied to green pottery. We also had a bucket full of a thin Tile 6 recipe which is mixed thin for dipping. It's possible that the other white slip in your studio is made with a ball clay. If that were the case, one reason for having the Tile 6 bucket is that it's a true kaolin slip.

 

There are many formulations of slip with completely different purposes. If one is thick and one is thin that solves the answer to your question. Thick slips are to be applied to wet or leather hard pots. They are mixed to a thick consistency where they can be painted on with a brush generally while the pot is on the wheel. The thin formulation of a slip is designed for application to bisque or green ware as a thin coat the same way a glaze is applied. These thin slips are generally made with at least a portion of the clay being calcined. Calcining means to bisque fire a powdered material prior to use in a slip or glaze. This calcining makes the slip able to adhere to bisque pots with out cracking off because it reduces the plasticity and shrink of the slip.

 

Another term to differentiate these is the word engobe, which is the thick version of slip often with a colorant added. Engobes are used in the decoration technique called sgrafitto where an engobe is applied to a leather hard pot and then once the slip is leather hard it's carved into revealing the clay underneath in contrasting color. Sometimes the thin dipping slips are also referred to as flashing slips which generally describes a slip with a slightly higher alumina content. The alumina in the flashing slips will help trap chemicals in an atmospheric firing and change color or "flash". These are used in wood, salt and soda firing as a form of decoration to the exterior of a pot in place of a glaze.