Pinholes are often caused due to the generation of gases from the decomposition of the organic materials present in the glazing mixture or escaping of the crystal water. Pits are often caused by the air bubbles trapped inside the clay body, which tries to escape after the glaze melting.
Why are there pinholes in my glaze?
If the body surface is rough (because it contains grog or sand, or the ware has been mechanically trimmed during leather hard stage opening imperfections in the surface), pinholes often occur as the glaze dries on the body. This is a poor lay-down and these raw pinholes may turn out as fired pinholes.
What is pinholing and why is it a problem?
Pinholing is a plague in industry, the tiniest hole in the glaze surface of a tile or utilitarian item can make it a reject. Industry goes to great pains to get materials of very fine particle size for their bodies and glazes to reduce the occurrence of glaze defects. They need to be sure that ware can survive their fast firing schedules.
What causes pinholes in clay to form?
Pinholes are often caused due to the generation of gases from the decomposition of the organic materials present in the glazing mixture or escaping of the crystal water. Pits are often caused by the air bubbles trapped inside the clay body, which tries to escape after the glaze melting.
How to prevent pinholing when glazing?
You can use the technique of ball milling to make your glaze stay uncontaminated for a long time. Using a ball mill can easily give you significant results and prevent pinholing and other glaze contamination problems. Also, clean the glazing tools after every use to avert contamination.
Why do I get pinholes in my glazed pottery?
Perhaps the most common of all glaze defects, pinholes are tiny holes in the glaze surface which penetrate all the way through to the body. They are caused by gases escaping from the clay body during the firing cycle, after originating from tiny pieces of organic matter, such as charcoal, which is present in the clay.
Will firing fix pinholes?
If ware is fired too rapidly the glaze melt may not have a chance to smooth over. If thicker or protected sections of ware have more pinholes this is usually an indication that slower more even firing will improve the surface over the entire piece.
What happens when glaze is too thick?
Fluid melt glazes will run off ware if applied too thick. Glazes having a thermal expansion lower than the body, and thickly applied on the inside of vessels, can fracture the piece during kiln cooling. Those having a higher expansion than the body will often craze if applied too thick.
What causes craters in glaze?
If the carbon in materials is not fully removed from the body, then gas will form during the glaze or decorating firing, forming bubbles or blisters. These may pop to become craters or pinholes. These defects can occur because: There was not enough air in the kiln during firing for the carbon to properly burn out.
How do you stop glaze Pinholing?
The main cause of pinholes in pottery is air bubbles created by gases in the Glaze or Clay body. You can minimize them by using finer particles, adding more flux, applying a second, thinner glaze layer, and using a well-ventilated kiln.
How do you stop Pinholing glaze?
In addition, a rough surface exposes pore networks inside the body to larger volume 'exit vents' that produce pinholes in glazes. You can prevent this by using a finer body, smoothing the body surface in the leather hard state after trimming, or by applying a fine-grained slip.
What happens if glaze is Underfired?
Overfiring and Underfiring Underfiring results in a dry, scratchy glaze surface. Pots that have been underfired can be fired again to a higher temperature, which may salvage the glaze. Overfiring results in glazes that begin to run.
How do you know if the glaze is the right consistency?
Your glaze should be the consistency of heavy whipping cream, thick but not too viscous. If you find that your glaze is too thick, try adding small amounts of water slowly, until it reaches the proper consistency. While adding water to your glaze, be sure you are stirring it constantly.
What ingredient do you use to thin out a glaze?
Powdered sugar, also known as confectioners sugar or icing sugar, sweetens the glaze and causes it to firm up. Any kind of liquid can be used to both flavor and thin out the glaze to a consistency that can be drizzled.
What does talc do in glaze?
Talc is used up to 60% in low fire artware bodies to increase thermal expansion so they fit commercial glazes. Talc is a refractory powder and can promote matteness and opacity when added to low-fire glazes.
What causes shivering in pottery?
Shivering is a ceramic glaze defect that results in tiny flakes of glaze peeling off edges of ceramic ware. It happens because the thermal expansion of the body is too much higher than the glaze.
Why does glaze flake off before firing?
When a glaze shivers it is under 'extreme compression' as it cools, peeling off the underlying clay body. This defect is most prevalent on pottery lips and handles, which are the areas of highest surface tension as the glaze hardens upon cooling.
How do you fix pinholes in paint?
Pinholes can only be repaired successfully by thoroughly sanding the substrate or by filling the holes with body filler.
Can you solder over a pinhole leak?
The most advanced pinhole leak fix involves cutting the pipe in half. But rather than a compression fitting, the plumber will use a solder fitting for the most secure repair. The pipe must be cleaned and free from the water first or else the soldering won't work. Flux is brushed onto the pipes and then placed together.
How do you fix pin holes in wood?
2:197:28The Woodpecker How I fill holes in wood - YouTubeYouTubeStart of suggested clipEnd of suggested clipI can mix wood filler with with dust and what I like about this kind of product is that I can add aMoreI can mix wood filler with with dust and what I like about this kind of product is that I can add a bit of water to make it even thinner. So after mixing this I can fill another hole.
How do you get rid of pin holes in paint?
0:141:51How to eliminate pin holes when coating overtop paint - YouTubeYouTubeStart of suggested clipEnd of suggested clipRun off like that real tight. Then you do it. Again. That's it real easy and your bubbles will beMoreRun off like that real tight. Then you do it. Again. That's it real easy and your bubbles will be gone it won't come back if you do it like that just want to do the other side.
Is the body the problem?
Do a sieve analysis of the body to determine if large particles are present. 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). If the particles are volatile (i.e. lignite, sulfur compounds) they will generate high volumes of gases at individual sites, possibly overwhelming the glaze's ability to heal itself there. The most practical solution is to either remove the implicated material from the body batch in favor of a finer particle grade (to distribute gas generation to more sites of less volume) or use a cleaner alternative (by cleaner I mean low-lignite and low-sulphur ball clays).
Is there a problem with the glaze recipe?
Glaze binders have been known to produce serious pinholing and pitting problems. Some decompose at higher temperatures than you might think. Switch to another binder that decomposes at a lower temperature, eliminate it if there is adequate clay to harden the dry glaze layer, or reformulate the glaze to melt later and more quickly using a fast-fire frit. Once again I ask, do you really need a binder, or could bentonite do the same job?
Is there a problem with glaze application?
If a glaze layer is too thin pinholes may be a product of a simple lack of glaze to heal them. Increasing the glaze thickness may dramatically reduce the pinhole population (of course your glaze must be stable enough not to run if applied thicker and it must fit well enough not to start crazing due to increased tension between it and the body). Keep in mind that what may appear to be pinholes may actually be blistering, this is often evident when increased glaze thickness reduces the pinhole count but reveals the remnants of many healed blister craters (dough nut shaped rounded bumps on the surface when viewed at an angle in the light).
Is the problem with the bisque firing?
Since most pinholes are the product of escaping gases, it is logical to bisque as high and as long as possible to eliminate the bulk of gases during that firing. The only disadvantage of bisquing higher is that ware will be less absorbent and thus may not be as easy to glaze. Find a good compromise temperature. Also, do not stack ware too tightly in the bisque and make sure there is good airflow in the kiln.
Is the problem spit-out?
If the surface of the glaze is covered with minute broken blisters then the problem is probably spit-out, a condition caused by expulsion of trapped water vapor inside porous ceramics on refire for luster decoration. It is amazing how long it can take to drive off all the water in a fast firing, it may still be coming off past red heat! Make sure the ware you put in a glaze firing kiln is dry.
Why is my glaze pinholed?
Once-fired ware is much more prone to crawling and pinholing because the glaze-body bond is more fragile after application and much more gas is generated during firing than for a body that has already be bisquit fired. Thus, while crawling is the most frequent complaint in once-fire glazed ware, pinholes are more common because of the significant out gassing associated with first-fire. If you add fast-fire to this mix sometimes it is a wonder that it is even possible to get a nice fired surface on a glaze! Try bisque firing to see if this eliminates the problem. If it does then the gases of firing a raw body are not being passed by your glaze; reassess the whole process to reduce all contributing factors as much as possible. Use a fast-fire glaze. See the article on blisters for related information.
Why is glaze viscous?
Most often a glaze melt is viscous because it is not melting enough. However even well melting glazes can have a chemistry that makes them resist flow (i.e. high alumina content) or they may contain a material like Zirconium that stiffens the melt because it does not go into solution. Using melt flow testers to gauge the melt mobility of your glaze is a good idea, it is very difficult to detect melt flow changes by simple inspection of a glaze layer. You might think that the melt is fluid enough, but only a melt flow test will say for sure.
What is the effect of flux on glaze flow?
Increasing flux content to produce a more fluid melt often works well to combat pinholes and pits. Sometimes very small additions of ZnO, SrO, or Li2O can have a dramatic effect on glaze flow. Sourcing fluxes from frit or using a finer particle size material will improve the melt flow also. Or, you could simply fire higher.
Why is my glaze pinholed?
Once-fired ware is much more prone to crawling and pinholing because the glaze-body bond is more fragile after application and much more gas is generated during firing than for a body that has already be bisquit fired. Thus, while crawling is the most frequent complaint in once-fire glazed ware, pinholes are more common because of the significant out gassing associated with first-fire. If you add fast-fire to this mix sometimes it is a wonder that it is even possible to get a nice fired surface on a glaze! Try bisque firing to see if this eliminates the problem. If it does then the gases of firing a raw body are not being passed by your glaze; reassess the whole process to reduce all contributing factors as much as possible. Use a fast-fire glaze. See the article on blisters for related information.
What happens if you don't use a fast fire glaze?
If you are fast firing and are not using a glaze formulated for fast fire then you will almost certainly be having glaze pitting and surface imperfections.
How to slow down a glaze firing?
an hour per cone at cone 6), soak if possible, and slow the initial cooling phase. If the glaze contains an early melting material (i.e. a high boron low alumina frit) you may need to slow the firing just before the frit begins to fuse to allow as much gas to vent as possible before continuing. Most frit suppliers supply melting or softening temperature information.
How to see if a glassy pool exists at its base?
Use a sieve to isolate some of the coarser particles and fire them to body temperature. Fire to see fi any of them are active melters. Examine pinholes under the microscope so see if a glassy pool exists at its base. If this is the case it is possible that a combination of vigorous melting activity and the resultant creation of a glass chemistry that resists pinhole healing could be occurring. In this case, the offending particles in the body must be eliminated or ground more finely.
Why is glaze viscous?
Most often a glaze melt is viscous because it is not melting enough. However even well melting glazes can have a chemistry that makes them resist flow (i.e. high alumina content) or they may contain a material like Zirconium that stiffens the melt because it does not go into solution. Using melt flow testers to gauge the melt mobility of your glaze is a good idea, it is very difficult to detect melt flow changes by simple inspection of a glaze layer. You might think that the melt is fluid enough, but only a melt flow test will say for sure.
How long does it take to ball mill a glaze?
Do not underestimate the value of ball milling to improve fired glaze surface qualities, many a problem with pinholing and blistering has been solved this way. Many companies ball mill up to 12 hours for best results.
What are the reasons behind pinhole formation & how to solve it?
Well, there is more than one reason that contributes to making the glaze look like a faulted one. Here are some of the reasons that lead to pinhole formation on the pot surface along with their solutions.
Why does glaze get pinholes?
Too much rapid firing doesn’t let the glaze set on the pottery body properly. And this causes the glaze to have a not-so fluidic consistency, preventing the clay from healing itself. It further leads to the generation of too many gases from the clay body, causing pinhole formation.
What happens if you mix glaze ingredients?
Most of the time, if the glazing ingredients are not appropriately mixed, then it is undoubtedly going to create problems post-application. If the glazing mix is thick enough or zinc and rutile content are high in the mixture, then it is going to thicken the glaze applied on the surface of the pot.
Why is my clay pot incompletely fired?
If the kiln’s firing schedule is too short, then eventually it is going to leave the clay pot incompletely fired. Most of the time, it is the inadequate escape of the gases while bisque firing that works as the anchor of the reasons behind pinholing. And the pottery clay can eliminate these gases only if you bisque fire it for a long time at a high enough temperature. But consequently, this action makes the ceramic less absorbent, which causes problems during glaze application.
What causes pinholes in pottery?
Most of the time, the clay body contains grog or sand on its surface, which forms pinholes on the pottery surface. And an immature or under-fired bisque aggravates this problem by turning the raw pinholes into fired ones.
Why is my post glaze firing pinholing?
Most of the time, large particles stay trapped in the glazing mixture that causes pinholing post glaze firing. The presence of compounds like lignite, sulfur, etc. eliminates the healing capabilities of the glazing material and contributes to creating such glazing mistakes.
How long does glaze sit in a kiln?
Also, it is essential to hold the kiln at the glaze maturing temperature for a longer time and let the glaze sit for 2 hours or more so that it sticks on to the pottery surface properly.
What if you just cannot solve a pinhole problem?
The cause is likely a combination of thick glaze layer and gas-producing particles in the body. Bodies containing ball clays and bentonites often have particles in the +150 and even +100 mesh sizes. The presence of such particles is often sporadic, thus it is possible to produce defect-free ware for a time. But at some point problems will be encountered. Companies in large production need to have fast firing schedules, so they either have to filter press or wet process these bodies to remove the particles. Or, they need to switch to more expensive bodies containing only kaolins and highly processed plasticizers. But potters have the freedom to use drop-and-hold or slow-cool firing schedules, that single factor can solve even serious pinholing issues.
How can you best tell if a base glaze is prone to pinholing with your body?
Testing for pinholes and dimples is often best done using a transparent glaze over a large surface and looking at the surface in the light. In this case, an open bowl is used. Heavy pieces like this are difficult to fire evenly and encourage under fired areas where pinholes are more likely to appear.
Why is this cone 10 oxidation iron-brown glaze pinholing?
The glaze is simply insufficiently melted. In cone 10 reduction the iron acts as a flux and it melts very very well , so there are no pinholes. But here it simply does not have enough fluidity to heal the disruptions caused as gases escaping from the body below bubble up through it.
What is an oversize particle?
Oversize particle is a fact of life in bodies made from refined materials and used by potters and hobbyists. Industrial manufacturers (e.g. tile, tableware, sanitaryware) commonly process the materials further, slurrying them and screening or ball milling; this is done to guarantee defect-free glazed surfaces.
What is the difference between Plainsman M340 and M340?
The difference is a slow-cool firing. Both mugs are Plainsman M340 and have a black engobe inside and partway down on the outside. Both were dip-glazed with the GA6-B amber transparent and fired to cone 6. The one on the right was fired using the PLC6DS drop-and-hold schedule. That eliminated any blisters, but some pinholes remained. The one on the left was fired using the C6DHSC slow-cool schedule. That differs in one way: It cools at 150F/hr from 2100F to 1400F (as opposed to a free-fall). It is amazing how much this improves the brilliance and surface quality (not fully indicated by this photo, the mug on the left is much better).
What is bisque fired to cone 06?
Second, the body was only bisque fired to cone 06 and it is a raw brown burning stoneware with lots of coarser particles that generate gases as they are heated. Third, the glaze contains zircopax, it stiffens the melt and makes it less able to heal disruptions in the surface.
Why is reduction gas firing so popular?
Reduction gas firing is known to produce much fewer glaze defects, the reason is often that the kiln, because of its mass, cools much slower. Some glaze chemistries are much more prone to pinholing. For example, high Al 2 O 3 and ZrO 3 stiffen the glaze melt making it less able to heal defects.
What is the most common glaze defect?
Crazing is the most common glaze defect, and normally the easiest to correct. In both crazing and shivering the eradication of problems relies on matching the thermal expansion characteristics of both body and glaze. In practice, the most effective ways to correct crazing are:
Why does my glaze keep crawling?
Crawling is caused by a high index of surface tension in the melting glaze. It is triggered by adhesion problems, often caused by bad application. It occurs where a glaze is excessively powdery and does not fully adhere to the surface of the clay. This can be alleviated by the addition of a small amount of gum to the glaze batch. Crawling is more common in matte glazes than in fluid ones; sometimes the problems of crawling can be reduced by the addition of a small amount of extra flux. Crawling can also occur when one glaze is applied over another, particularly if the first is allowed to dry out completely before the second application. Some fluxes, particularly zinc and magnesium, are likely to cause crawling when used in excess. Calcining all or part of the zinc can help this problem.
How long to soak glaze in kiln?
hold the kiln at the glaze maturing temperature for a soaking period of up to two hours
Is it true that one person's fault is another person's fancy?
It is especially true in the ceramics world that one person’s fault is another person’s fancy–especially when it comes to glaze defects. Many ceramic artists deliberately create faults in their glaze surfaces to achieve a particular aesthetic. But, of course, there are some cases in which a glaze must be perfect for reasons of safety or hygiene.
Why does ceramic glaze blister?
Harry Fraser, in Ceramic Faults and their Remedies, states blistering (craters and bubbles) are caused by overfiring which causes the molten glaze to boil and generate the same type of bubbling that is seen in pots of boiling water. Possible causes include wares placed too close to elements, resulting in blisters in the area close to the element, very rapid firing as the glaze and body approach maturity -- especially in low thermal mass kilns that tend to cool very rapidly that results in bubbles and craters being frozen before the glaze has had time to flow and clear the defects in its surface, presence of some oxides (manganese especially) and carbonates in the glaze that alter their state during oxidation and release gases which may cause pinholing (more often) or blistering (less often). Fraser recommends a longer soaking period or a slower firing cycle over the last 122 degrees F of the glaze cycle.
What is the best firing temperature for bisque?
In general, I would bisque everything to 04. Pinholes typically need a soak or higher firing. Blisters typically need a lower firing or the glaze needs to be stabilized with more clay and/or silica.
How long to hold bisque for pin holing?
some people believe firing to a slightly higher bisque and hold for a 1/2 an hour will eliminate gases that cause pin holing. If you go back and look at the topic pin holing in past posts you'll find a huge discussion about this.
Why do we fire to 04 bisque?
we fire to a 04 bisque which helps to alleviate some issues but in the end we've had to abandon a few glazes because of blistering/pinhole issues.
Why does my kiln run cold?
Your kiln has graded elements. The top and bottom elements run hotter to account for heat loss out the floor and lid. Glaze problems at the bottom could be from the bottom running hotter or colder. More likely colder. The thermocouple is only reading temp in the middle, so if the bottom is packed too tight, it can run cold. Put in cones bottom, middle and top to verify evenness.
How many firings does a thermocouple have?
The thermocouple is brand new (~6 firings), and I have just replaced the elements.
Does refiring glazes work?
re-firing, in my experience, does not work. every glaze has it own personality so hopefully you have some success. we've only ever tried re-firing to the same temperature as the initial firing but we were only trying to fix the most severe cases.
