Engobe recept
Engobes can be defined as liquid clay slips of varying compositions which are applied to the surface of a clay object, e.g. a pot. The purpose of the engobe can be as different as the varied forms it comes in: to give color to a piece; to improve the surface texture; to provide a ground to do further decoration on; to add textures. No tracking! No ads! All Articles. It can be difficult to find an engobe that is drying and firing compatible with your body.
It is better to understand, formulate and tune your own slip to your own body, glaze and process. Non-glaze slips referred to as engobes when applied thickly for pottery and tile decoration have long fostered great fascination. Almost everyone has marvelled at the simple beauty of terra cotta ware decorated with white slip and finished with a transparent glaze. Many potters are adapting this age old process to stoneware and porcelain.
Industry, especially tile, routinely applies slips and engobes e. They are almost universally used in the single fire process. This is logical since their key application is to cover over dark burning or dirty bodies made from local materials, in these cost conscious situations it makes little sense to fire more times than needed. Pairing of engobe-thickness slips with a specific body is difficult so recipes travel even less well than glazes.
They need to be drying, firing and thermal expansion compatible with both the underlying body and overlying glaze.
Each of these should be tested individually. Compare this to a glaze being applied directly to a bisque body: you only need to focus on thermal expansion compatibility with the body; this is so much easier. Consider the first major challenge: Adhesion with the body both in drying and firing , getting the stuff to stick on! If the slip is applied thick enough and does not shrink at the correct rate or amount during drying and firing, cracks will develop or it will flake off.
No matter what logic, theory or lab instruments might indicate or what others might advise, if cracking or flaking is occurring it is much more likely you need to react by adjusting the recipe appropriately than by adjusting the way it is prepared or applied. Different factors are involved in attaining compatibility for firing and drying and a change that improves one aspect of fitness may detrimentally affect another.
L3685U - Cone 03 White Engobe Recipe
While each material in the recipe is there for a drying, firing, adhesion, thermal expansion or aesthetic reason, it is also potentially detrimental to one or more other parts of the process; this means developing the right recipe is a real juggling act. The most obvious use of a fine-grained white engobe is to cover a dark colored and possibly coarse-grained body so that brightly colored or lightly shaded glazes appear as they do on fine porcelain.
The tile industry is by far the largest user of engobes, it is very common for them to use red burning clays they are often locally available and fire much stronger than light burning clays at low temperatures. They cover the red bodies with a white burning opaque engobe. Obviously good adherence to the fired body is paramount, so the engobe needs frit or other melters to create a glass bond.
Adherence will obviously be best on vitrified bodies where an interface can develop if the body does not vitrify well extra frit will be needed to create a more glassy interface, but not so much that opacity is lost. The fired interface between slip and body will never be as good as one between glaze and body. This is potentially a weakness if the fired adherence of the slip is not evaluated and optimized.
Since slips do not melt formulation is normally done on the recipe level the physical properties must simply be observed, ceramic calculations are not really applicable. You need a different mindset than with glazes to have success with engobes. Glazes smooth out when they melt, engobes do not. Like paint, the surface you apply is the one you get after firing. Thus drips, variations in thickness, roughness, pinholes , bubbles, etc are going to show.
Engobes Tutorial: The Engobes Basics
Normally a glaze over-layer is not going to be thick enough to cover over problems in the slip laydown , infact, slip irregularities can produce glaze defects. Application for tiles is straightforward since the surface is flat and horizontal, but for uneven shapes it is a lot more complicated. Here are some ideas. Conceptually a recipe can be as simple as a porcelain body with enough added frit for adherence but no so much that glass development reduces the opacity.
This can be a fine line. It is better to mix your slip as a recipe of ingredients that include those for the porcelain rather than just adding something to a powdered porcelain whose recipe you do not know, this will give you the needed flexibility to adjust. For high temperature you should be able to flux using feldspar and other raw materials rather than frits e. If it can be more mature , try 40 feldspar at the expense of silica this time.
The idea is to tune it degree of maturity to get maximum melting without loss of opacity. If the slip is too plastic, use calcined kaolin for part of the clay complement if needed to cut drying shrinkage. And as a last resort use gum to harden it and give better flow however it is better to adjust or substitute clays to get the flow and drying properties needed, gummed slips dry slower.