User:Rosella1356/Leather-hard

The leather-hard stage is the easiest place to add on extension material that cannot be dried with the rest of the pot without causing some issues to occur. For instance, in some cases when handles are added before the base and sides have been dried, the handle can dry before the sides do and cause cracking as the weight of the dried portion is no longer at the same equivalence with the wet side. The same goes for other additions to the pot that will not dry at the same rate as the rest of the pot. These include bases that are not the same shape as the rest of the vessel, hand holding additions, or decorations on the sides.

The leather-hard stage of a clay bodies drying process. Without getting it to a stage where most water is gone from the surface, the future ceramic is much more likely to crack or blow up in the firing. This additional step in the drying process also allows for a certain room for error. In the leather-hard stage the clay can be returned to a plastic form by adding the water. The certain amount of water is determined by its water of plasticity level.. The water of plasticity is determined when the clay is at optimal plasticity, which means that it can be shaped by hand or wheel without it becoming to wet to hold together. This nature of the leather-hard state is what allows for it to be a safety net for newer potters and experienced potters, who want to ensure that no vessel is ruined in a fire when it could have been avoided in the first place by drying it in sunlight or a uniform room first.

This is the best stage for attempting to carve decorations onto the vessel as well.. It won’t crack the pot, but it also won’t require trying to force the clay apart while still wet. Most clay do not like leaving holes in between the sides because of the fact that the properties of plastic tend to revolve around needing to touch the other particles to slide around. Equally it is possible to change the perception of the texture of the pot during this stage by either highlighting the clay's natural textures, or by smoothing over to make it into a pore smooth finish. These decorations are often how scene depictions are shown on a vessel. Glazes or ceramic glaze and paints can do wonderful jobs showing pictures of scenes, but they will fade with use, whereas carved decorations will last as long as the vessel itself does. Decorations on vessels has been a common trend throughout the history of ceramics as most of the pieces that have been found have some form of glaze or carving on them. This brings up the interesting point that more than likely those earlier civilizations utilized the leather-hard stage before firing their vessels. It makes one wonder how much more information, archaeologists would have been able to find if leather-part ceramics weathered time as well as fired vessels do. After all ceramics are a large part of archaeology.

Other processes that can occur while the pot is in the leather-hard state include both glazes and slips. Slips are when water is added to clay at a level higher than the rate of plasticity, so that it becomes a viscous liquid that can be applied to add additional shapes to the side of pots. However, be careful when working with slips as it it is a silica base material that could be hazardous if inhaled. This can add a layered effect onto the pottery itself. Glazes are a glassy coating that can be applied like a paint to a vessel when it is either leather-hard or briefly fired. When glazes are applied in the leather-hard stage, they tend to run a lesser risk of cracking the pot when they are fired because the glaze can be allowed to dry before the firing is continued, however there are still instances when the glaze will crack no matter what is done to prevent it due to any number of changes that could happen during a firing.. When the pots have been fired before the glazes are put on, they are referred to as biscuits. It is important not to mix up the term leather-hard with biscuit (pottery) despite the fact that it may seem as though the two are similar, only one can return to a plastic state if an error is made, and that is the leather-hard vessel. In fact a biscuit while looking similar to the leather-hard vessel has actually been fired to around 1652°F to 2012°F, which is why the biscuit cannot return to its plastic state any more than any other fired pot. Another process that can occur while a vessel is in the leather-hard state is to fettle the vessel. Fettling is when some trims the edges or casting marks that are on the pot from the initial molding of the vessel. This allows for the pot to gain a smoother texture.

While in the leather-hard stage, some vessels can be modified to give extra characteristics that are desired. One additional aspect to a vessel that can be made is to make the vessel into a lute. A lute in terms of ceramics is two pieces of leather-hard clay placed together with a slip acting as a glue. These lutes increase the overall strength of the pot, which allows it to withstand more stress than other pots that have not been formed into a lute. This stress can be shown on the stress-strain curve. Another aspect that can be added to a leather-hard state is burnish, which is done through a process referred to as burnishing. Burnish is when a hard object generally made of glass is rubbed on a leather-hard vessel to smooth all the clay particles into facing the same direction that allows light to reflect off them. Similar to burnish, is polish. This is done extremely similar to burnishing, only instead of trying to force the particles of the clay to move into facing the same direction it just smooths over the edges to make it glossier in nature without an actual glaze. In a process called polishing, which gives rise to similar styles but ultimately is not as stylized as burnishing. Another option is combing, which is when a tool is scraped down the side of a vessel to make indentations that are uniform throughout the vessel in width and length.

The most important aspect of the leather-hard stage is not in any of the things that it can do for the field of pottery, or even what ceramics do as a whole, but in what this means for the substance itself. In nature, there is only one material that can change forms while maintaining shape as the leather-hard form of clay does, and that is clay. Clay is the most important part of this definition because clay itself has had such an enormous impact on human existence. Clay is what helped us store food to have villages instead of constantly roaming. Clay is what helped us build houses. Clay built civilization, and it should be recognized for what it did for all of humanity. Leather-hard is just another portion of the wonders that clay brings.

References

Rice, Prudence, “Pottery Analysis”, 2nd ed., 2015, The University of Chicago Press.

Flight, Graham, "Introduction to Ceramics", 1999, Prentice Hall Inc.

Mills, Maureen, "Surface Design for Ceramics", 1st ed., 2008, Lark Books