Weigh, fire to cone 04, and re-weigh a sample of the coarse particle material to see if it loses significant weight (due to decomposition and associated gas generation). This may be an opportunity to make your process better and more stable.Īre large particles or gas producing materials present?ĭo a sieve analysis of the body to determine if large particles are present. If reading this article makes it clear that there are some things that you have been overlooking, then the success you have had up until now might be accidental. If a pitting or pinholing problem has started to happen and it has not occurred before do not assume that there is some new problem. Keep this factor in mind as you read the material below, the world you are in will determine the validity of the comments being made. Some are using prepared bodies and/or glazes and thus have less flexibility to change things. Strangely, even though small scale producers fire much slower, they can have just as many problems with pitting and pinholing. Industrial producers must find ways to fire quickly, often in an hour of less. Hobby and small scale producers have the flexibility to do much longer firings and generally must do so for the lack of fast-fire equipment and materials. Being careful to apply a dense even lay down of glaze. Selecting glaze materials that decompose to form less gases.Making the glaze more fluid or altering its surface tension to enable it to better heal itself.Providing more kiln draft to oxidize and carry away products of decomposition coming from the body or glaze.Giving the glaze time to heal by soaking or slower cooling.Giving the gases more time to escape by slower firing or using a fast-fire glaze that melts later.Distributing body out-gassing by finer grinding.Reducing burn-off by higher bisque or cleaner body (less lignite for example).Still most strategies to eliminate these involve attack on several fronts: Generally a true pinhole is a problem with the body that extends up into the glaze whereas a pit could be considered a problem with the glaze or the firing. When pinholes or pits occur there are often more than one contributing factor. In the following I may confuse pinholing and pitting or may neglect to mention one or the other, I apologize for this. Keep in mind also that larger pinholes may actually be crawling (see links to other articles). The causes of pinholes can often be similar to those of blistering. If ware is glazed these gases may need to bubble up through the glaze melt, depending on how early it begins to melt. During firing bodies typically generate gases associated with the decomposition of organic materials and other minerals, escape of crystal water, etc. Pinholes or pits are often no larger than the head of a pin. 'Pits' are smaller, they mar the surface but to not penetrate all the way down. 'Pinholes' are small holes in the fired glaze surface penetrating down to the body below, often into a surface pore or opening.
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