Trouble-Shooting in Ceramics

Body Bloating | Body Cracking and Dunting During Firing | Clay Cracking During Drying | Clouding in Transparent Glazes | Dealing With Chrome Flashing | Foaming of glaze slurries | Glaze Blisters | Glaze Crawling | Glaze Crazing | Glaze is Off-Color | Glaze Marks or Scratches | Glaze Pinholes, Pitting | Glaze Shivering | Glaze Slurry is Difficult to Use | Glaze Staining | Over firing | Powdering, Cracking and Settling Glazes | Specking | Uneven Glaze Coverage

Troubles

It important to be in control of your process and understand it to troubleshoot problems well. If not you will not know how to ask the right questions that will bring the needed answers. Production problems are often blamed on the materials so we attempt to examine this in this area of the database. There is no question that machines, kilns and the people who operate them are responsible for alot of production issues but that will be dealt with to a limited extent here.

Admittedly if materials are not consistent then variation in them will definitely be a cause of many problems. But if you think the materials are different is it because you are testing the properties critical to your process and have numbers to prove it? If you depend on consistent materials can you afford not to be testing? If the materials are consistent then you must learn to adapt your equipment and people to them and to articulate what properties need to be adjusted and how. It is interesting that many factories around the world employ materials that others might think would be impossible to use, but their secret is adaptation, knowledge and experience. Early in the planning stages of any production project there should be an assessment of the available materials, especially what their strengths and weaknesses, are so that a production line can be adapted accordingly or these materials can be blended with imported ones to move properties in the needed direction.

It is important also to appreciate, of course, that different types of product produced using the same process and equipment present varying challenges. However the level of difficulty is often under estimated. For example, if you produce plates of diameter x and want to produce larger ones, the amount of cracking and warping problems will increase at a dramatically higher rate than the size. Plates that are 25% larger might have 100% more problems using the same process. Likewise, if you are not testing the firing response of your body at temperatures that are higher and lower than your production temperature you might not be aware of how volatile its color response is, for example, when overfired. Likewise problems like warping, bloating, cracking can be lurking just beyond the boundaries of your process and small changes in materials or process could bring dramatic increases in reject rates.

It is possible that you have operated for many years making a specific product using the same production machines and the same procedures and materials. Such situations can breed complacency and routine testing may be discontinued (and even technical staff dismissed or not replaced). Many plants have also become increasingly dependent on consultants and technical support from suppliers. While these have a place, you need to be watch day-to-day and be able to react quickly to production problems. The secret is being able to ask the right questions to find the cause (or more likely the causes). If you are having many problems chances are you are not doing routine testing. For each of the problems in this area we have provided links to tests you can do to avoid these problems in future.

Links

Articles Understanding the Terra Cotta Slip Casting Recipes In North America
This article helps you understand a good recipe for a red casting body so that you will have control and adjustability.
Articles The Black Art of Drying Ceramics Without Cracks
Anything ceramic ware can be dried if it is done slowly and evenly enough. To dry faster optimize the body recipe, ware cross section, drying process and develop a good test to rate drying performance.
Articles Firing: What Happens to Ceramic Ware in a Firing Kiln
Understanding more about changes are taking place in the ware at each stage of a firing and you can tune the curve and atmosphere to produce better ware
Articles A Low Cost Tester of Glaze Melt Fluidity
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.
Articles Understanding Glaze Slurry Properties
It is possible to have a glaze slurry that is a joy to use, but only if you understand the physics of the materials in the glaze recipe.
Articles What is the Glaze Dragon?
At Digitalfire we use a Dragon to personify the kinds of thinking that prevent potters, educators and technicians from understanding and therefore controlling their glazes.
Articles Understanding the Deflocculation Process in Slip Casting
Understanding the magic of deflocculation and how to measure specific gravity and viscosity, and how to interpret the results of these tests to adjust the slip, these are the key to controlling a casting process.
Materials Kaolin
Tests Shrinkage/Absorption Test
Glossary Mechanism
Identifying the mechanism of a ceramic glaze recipe is the key to moving adjusting it, fixing it, reverse engineering it, even avoiding it!

By Tony Hansen


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