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jo4550

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jo4550 last won the day on April 21 2011

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About jo4550

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    http://johanna.demaine.org

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  1. There is no reason why you shouldn't fire decals in a gas kiln. The main thing is to have a very slow temperature rise to 400-450.C so that all the combustibles can burn out. At all times keep the kiln in an oxidizing atmosphere to 800.c. You need to keep a clean atmosphere so even over-oxidiziing is advisable. For many years I fired both lustres and decals in my gas kiln very successfully. Johanna
  2. Duncan Gold Luster Question

    You may find that lustre on stoneware fires better at the higher end of the lustre firing 800-820.C. If you come across any books on lustre you will find that different firing temperatures are given for different categories of glazes. These categories are usually glass, earthenware, soft paste porcelain, hard paste porcelain. Stoneware falls within the hard paste porcelain range of firing temperatures whereas cone 6 glazes would fall within top end of soft paste porcelain. Lustre relies on bismuth oxide to flux or bind to the surface of the glaze. Johanna
  3. is gilding / gold leafing food safe ?

    The best way to remove purple spots is with a gold eraser.
  4. Duncan Gold Luster Question

    It doesn't matter what brand of gold or lustre you are using you should not be present in the same space as the kiln when you are firing these. The toxicity of gold fumes is present till at least 450.C. You will notice that is when the smell also disappears. You should never work in the same space as a kiln when it is being fired. Fumes are being emitted all the time.
  5. Silver Lustre

    Silver lustre tarnishes. Nowadays industry uses platinum lustre instead as it does not tarnish.
  6. Decal Help Please!

    Stephen, ceramic toners will not work in a conventional laser printer. The printer needs to be altered to accommodate the use of the ceramic toners. I believe some Ricoh printers are retrofitted for this. The polymers (plastic bead like substances) adhere the colours to the decal paper. Mason stains are not milled fine enough for laser toners and they need to be mixed in specific proportion with the polymers. There are also 2 different systems out for ceramic toners. One has a flux in the toner mix which allows the decal has at approx 800.C. The other has a flux in the covercoat which is applied after the printing. This allows the decal to be fired at the temp required, eg for glass, overglaze or inglaze temps. Regards Johanna
  7. Decal Help Please!

    To determine compatibility with laser printers, look up the MSDS sheet for the toner cartridge the specific model uses. Some laser printers use polymers as the main pigment ingredient. These won't work. Others use iron, listed as ingredients beginning with the prefix "ferr." This what to look for. The HP I have uses 45% iron in the toner pigment. As I understand it the polymers, when melted, are the binder of the colourant to the paper in laser printers. Originally carbon was used as the colourant for black and this is still used by most laser printer manufacturers. However HP definitely uses iron oxide (also written as ferrous/ ferrous/ferrite) for their MONO laser printers. To add to this, the reason a colour laser is not suitable, is that the printer drum has to go to a higher temperature to melt the polymers used for the other colours. This higher heat melts the laser decal paper onto the drum thus rendering the printer useless. Regards Johanna
  8. is gilding / gold leafing food safe ?

    Hello Kennedy It is normal for some glazes to change on a refire especially when you are approaching the softening point (I do not mean melting point) of the glaze. This is the point where the fluxes start to be active. This has become very obvious when running the laser decal classes and searching for the softening point for the decal to adhere. There is a fine line where the glaze doesn't react and this is at the lower end of the temp scale. I would hazard a guess that your glaze has a flux that has a very wide firing range and it is perhaps Gerstly Borate. You seem to have reached a point at cone 06 in your glaze where the glaze is already outgassing and the cooling at 06 halts the process and and traps the gases changing both the colour and the integrity of the glaze. To resurrect this glaze AND burn off the lustre find a cool spot in your glaze firing and take back up to top temp. This should restore the glaze. I say cool spot as refiring is almost like going a cone higher than the original firing. I would have attempted to save the gold and platinum surfaces by adding a couple more layers (with firings in between) and firing to your gold firing temperature before I took the drastic step of burning the lustre off. To remove small areas of lustre it is common to use a gold eraser but it has to be used carefully as you can "matte" the surface of the glaze that you are rubbing. Lustre can also be removed by using hydrofluoric acid but I personally wouldn't go down that path for H&S reasons. It also mattes the surface of the glaze where the lustre has been removed. Cheers Johanna
  9. There are a couple of issues here but I would like to start off by pasting an excerpt from the Heraeus fact sheet on Lustres as I have run out of space to add any more attachments. This can be found in its entirety at http://tinyurl.com/lvt6m7c Heraeus is one of the largest overglaze and lustre producers/suppliers in the world. They are based in Germany. 1 General Information Lustres are based on metallic compounds dissolved in organic solvents. After firing they form a very thin layer (less than 0.1 μm). Typical characteristics of lustres are their brilliance as well as their metallic iridescent brightness which occurs after firing on smooth substrates. The lustre loses its iridescent effect on matt surface and appears matt. Lustres are suitable for the decoration of glass, porcelain, bone china, earthenware 2 Firing Range 480-630° C / 896-1166° F for glass and lead-crystal. 650-900° C / 1202-1652° F for porcelain, bone china, earthenware and tiles. 3 Precious Metal Content Lustres contain less than 6 % precious metal or are precious metal free. 4 Properties 4.1. Mechanical Resistance The mechanical resistance of lustres does not achieve the same standard as most ceramic colours and precious metal preparations because the formed lustre film is very thin. Therefore, we recommend that customers test the decorations under their own conditions to achieve the required resistances. From this excerpt you will see that lustres applied to tiles used as a splash back may be a short term measure as constant cleaning with an abrasive will soon wear off the lustre. However I am assuming that you have taken this into consideration. I am finding it hard to get a good image of the tile to show that it has a creamy base so I cannot comment on how many firings this would have had but I suspect only one overglaze firing. As you can see from the excerpt lustre can be fired anywhere up to 650-900° C / 1202-1652° F depending on the surface it is on. The controlling factor is the softness of the glaze that it applied to at the temperature you are firing to. The softer the glaze becomes the more the lustre will sink in. This is especially so for low earthenware glazes. As I have said in previous posts Duncan products are rarely, if ever, used by the porcelain painters (the main users of Overglaze techniques). They buy products that are are manufactured by the suppliers and not just repackaged and rebranded as in the case of Duncan overglaze products. I have also never heard of lustres being described as Lustre Overglaze. Regarding Duncan's instructions that you supplied here are my thoughts. 1. Any glaze or surface is overglaze compatible. (I don't understand the need for this statement) 2. The firing temperature is suspect. Maybe it is a typo and it is meant to be cone 016. I don't know whether they are offering a normal lustre because lustres starts to burn off after 900.C and they state to fire to 1000.C I would normally recommend firing a cone 6 glaze to 760-780.C however I have refired them successfully to 810.C In your situation where you will need extra mechanical strength I would suggest you run a test and see how the cone 6 glaze interacts with the MOP at 900.C. It is a chore but you won't know until you try as each glaze behaves differently. The MOP that I use is a Fay Good product and can be purchased in the USA from China Painting today. Here is a direct link http://tinyurl.com/mg3ml75. #Ceramics Monthly January 2013 contains a techno file on Lustres #Pottery Making Illustrated May-June 2013 has an article on how to use lustres. Johanna DeMaine
  10. Here is a youtube link of an old Wedgwood 1930's film that shows you the sprigging process. Here is also a link to 2010 CAD archived feature on sprigging http://ceramicartsdaily.org/education/ceramic-art-lesson-plan-making-sprigs/ Johanna
  11. Hello Sue What you are describing is quite prevalent in refiring glazed ware at at China paint temperatures. It is often called mildew but it is actually black spotting that occurs on the UNGLAZED surfaces when the clay body has NOT been fired to full maturity. Hence you will normally find it under the work (where it touches the shelf)and footrings. It is not trapped carbon from poor bisqeing. It is mostly found in older pieces that have been around a while. It is carbon being trapped in the open pores of the body and this can be generated from a variety of sources. The carbon can become reabsorbed and trapped from the media being used so it is more prevalent to occur from oil based mediums than water based mediums. This coupled with poor circulation and ventilation in the kiln during firing allows the pores of the unglazed clay surfaces to reabsorb this new carbon. This carbon can be burnt out with repeated firings especially if the temperature is raised slightly higher. The easy answer to all this is that if you are making things from scratch make sure you fire to the full maturity of the clay or otherwise get a clay that vitrifies at the temperature you want to fire to. Then this problem shouldn't occur. Always make sure you have the lid or door of the kiln slightly ajar in the overglaze firing until at least 650.C This allows the gases generated from the mediums to be dispersed. Always allow plenty of space between the shelves in the kiln during an overglaze firing. Always try to fire to the highest temperature in your overglaze firing depending on your glaze type. eg if using porcelain fire to 800-820.C rather than the lower 760-780.C option. This allows more carbon to burn out. If at all possible fire your pieces lifted OFF the shelf by little wads or pins. I have attached a small .pdf made from page 125 of "Ceramic Faults and their remedies" by Harry Fraser. This deals with this topic in greater detail and it saves me from having to type it all out. Black spot.pdf Regards Johanna Black spot.pdf
  12. is gilding / gold leafing food safe ?

    Hi Kennedy You seem to be on the right track with your choice. Here is an extract from an article I wrote called "Health and Safety and Overglaze (in paticular lustres)" which is reprinted here on my website http://overglaze.dem...rg/?page_id=460 "My method of protection from fumes is as follows. I use a fume booth constructed by my husband together with a respirator while I have developed a method of working that limits my exposure to the hazards involved. I use a resist method whereby I estimate that 90% of my time is spent using lustre resist which is quite inert. The other 10% is the actual application of the lustre, as all the fine lines apart from some gold pen work is achieved by resist. I am confident that I am limiting my exposure to lustre. As well as this I wear a respirator. It is a Norton brand 7700 series silicone half face mask model with 2 N7500-1 organic vapour cartridges. It is extremely comfortable to wear despite the fact that I wear glasses. These cartridges are not suitable for clay dust etc. For that you need a particulate filter. However it is not enough to just wear the respirator. It must be maintained. When you have finished using it the inside must be wiped and then the whole lot stored in a sealed (clip lock) bag). This extends the life of the cartridges and keeps dust out. The cartridges need to be replaced when fumes can be smelled through the respirator. Norton has recently been taken over by North Safety Products. A web link to view is http://www.westernsafety.com/newnorthrespirators/newnorth1.html" Regards Johanna
  13. is gilding / gold leafing food safe ?

    http://chinapaintingtoday.com/store Look under Precious metals. I can recommend the Fay Good 12% liquid bright gold. It is a German product. It is the one I use. Another link to gold is http://www.thegoodstuff.com/ghlb1.html. This is also a German product. Germany has a history of producing the best gold. Golds and lustres are best bought from China/Porcelain painting suppliers. I don't know of too many painters who use Duncan products. They are aimed more at the hobby market. Regards Johanna
  14. Glaze Problem on slipcast items

    Several questions spring to mind here. How are you glazing? Are you glazing the inside and outside separately and in what order. If so what is the drying time between the inside and the outside? Are you brushing on the glaze? Are you spraying the glaze? I ask these questions as it seems to me that you may have a problem with crawling (glaze pulling away from the surface during the firing). I have experienced this when dipping glazes on thinly constructed work. The bisque becomes saturated when more glaze has been added to a surface. Bubbles or blisters appear on the unfired glaze during drying. These can be smoothed back by rubbing. However in the majority of cases the glaze crawls during the firing because of the lack of adhesion of the glaze to the surface. With brush on glazes this can also occur when subsequent layers can lift off the first layer be it ever so slightly. With sprayed glazes this can also happen when too thick a layer is applied in one hit rather than several thinner layers. One way or another the bisque can becomes saturated. Saturated areas do not have good adhesion with the glaze. With reference to your statement "about 70% of the problem pots have the problem on the side facing the elements" it may be that the side facing the elements initially heats up at a more rapid rate than the rest of the pot and trapped moisture causes further problems with poor glaze adhesion. I note also that your bisque temperature is higher than your glaze temperature. Could this be contributing to the poor adhesion? Regards Johanna
  15. Australian substitute

    Of the 3 main Ball Clays available in Australia (Ball Clay FX, Ball Clay R and Clay Ceram) Ball Clay FX has a very similar Chemical analysis. The TiO2 content is fractionally more whilst the Fe2O3 is slightly less. I have successfully substituted Ball Clay FX for OM#4 in glazes tests. However which ever you choose should be tested first as analysis change depending on what part of the pit is being mined. I have found the Glaze Program Matrix by New Zealand ceramist Lawrence Ewing to be spot on. This program has analysis of all the main materials used in Australia. It's database of materials used world wide is extensive. It is really easy to substitute Australian materials for materials used elsewhere and make the necessary adjustments. It is the best money I have spent on glaze calculation programs for my needs in Australia. Johanna
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