Soren Posted August 21, 2018 Report Share Posted August 21, 2018 After testing stain/oxide coloration and concentrations with small disks, I applied glaze to part of each disk to complete the test. Clay used is Standard 100 low-fire earthenware, bisqued to ^04. Glaze is Laguna EM-1130 Clear ^06. Top left quarter of the disk is with one brushed coat, bottom left quarter is with double coat. The kiln I used was an electric kiln with manual dial controls (two tiers, two dials, size about 2'X2'X2' outside and 17"X17"X20" inside). Firing included a cycle for 2 hours on "low" to drive out any water from glazing and preheat the kiln, 1 hour on setting "4" and the rest on setting "6" until maturation of the cone (Orton small bar ^06) and release of the kiln sitter switch. During the "low" cycle, the lid was propped open about 3". There are 4 peep holes in the side, and I left the middle 2 plugged and top and bottom unplugged for the entire fire. The test disks were on two shelves, one about 3" off the floor of the kiln and the other about 4" above that and slightly below the kiln sitter. I forgot to get the information from the kiln serial plate, but could get this information if it would be useful. Every single test disk came out with the same glaze result: tiny bubbles in the glaze cause a milky whiteness and loss of transparency in the glaze, which is not my desired result. Picture results may help: Does anyone have suggestions towards what is happening here? How can I avoid the bubbles in the future? More information/questions on what I think may be affecting the glaze: The glaze has been sitting for about 8 months since last use. There was some hardpan on the bottom, but I stirred the glaze and shook the jar until it seemed evenly mixed. Should I have added a deflocculant to ensure proper mixing and suspension of particles? The glaze seemed thick when I applied it. Should thinning the glaze with water allow for better brush application in thinner coats? Are the bubbles possibly caused by too thick an application of glaze? Is the glaze not maturing properly? I did not use witness cones, so I am putting a lot of trust (maybe foolishly) in the kiln sitter cone (which came out at a near-perfect 90-degree angle). I should probably use witness cones until I am very familiar with this kiln to ensure proper firing heat cycle. I do not yet have a thermo-couple, so I have no record of temperature. The exact firing time is also unknown, as I was not in the shop when the switch dropped. Total fire time was less than 7 hours total, as the switch had dropped when I checked at this time after the start of firing. Is there some way to allow for a soak with a kiln sitter near the end of the firing to allow more time for the glaze to move and smooth out? I am re-firing a few items to see if this helps. Included in the firing were two ocarina prototypes, one of which had a fair amount of pin-holing and the glaze had the same milky bubbles. I suspect the pin-holing is due to thick glaze application from brushing, but I am not totally sure. This pin-holing issue is also very important for me to resolve, as I want no pinholes on the final ocarinas. As a hobby ceramicist, most of my work to this point has been by trial and error, and I have tried and error-ed more things than I should without education. At this time, I am trying to study the science behind the processes I want to use in order to learn how to avoid so many errors, but I am still an amateur ceramicist. Thanks for any help, Soren Link to comment Share on other sites More sharing options...
neilestrick Posted August 21, 2018 Report Share Posted August 21, 2018 For starters I would fire hotter, cone 04. That may solve all the problems. Link to comment Share on other sites More sharing options...
Denice Posted August 21, 2018 Report Share Posted August 21, 2018 I can't tell from your photos whether you used a clear glaze but I know it will be milky if it applied to thick. If you are using a red clay that can also cause problems with the glaze. I would try firing first at 04 first before you change anything. Denice Link to comment Share on other sites More sharing options...
Soren Posted August 21, 2018 Author Report Share Posted August 21, 2018 11 minutes ago, neilestrick said: For starters I would fire hotter, cone 04. That may solve all the problems. Thanks for the recommendation, Neil. I considered this, but I want to be sure I do not melt off glaze and damage my kiln or accessories. My test kiln is older and already visually (not functionally) damaged, so I will test in that kiln. Two more questions: Should it be fine to refire the test disks to ^04, or should this be for future tests? Is there any way to determine the drip/run point of a glaze other than through experimentation? 1 minute ago, Denice said: I can't tell from your photos whether you used a clear glaze but I know it will be milky if it applied to thick. I used a clear glaze, and I suspect most of my issue is from thick application. When I first started my ceramics adventure, I bought some used glazes cheap on eBay. I discovered later that the seller probably refilled each jar with water to make them seem full. This allowed for my earliest glazing to be nearly flawless, as my brushed coats were thinner and more even. The thickness of the glaze became noticeable when I bought my first glazes from Laguna and started to have brush-application issues. I should probably water-down most of my glazes more in order for more even brush-application. It seems odd that I would need to take a stock "^06" glaze and fire to ^04, but this type of consideration is what is driving more research into the science of mixing my own glazes and clay bodies rather than stock materials. I also need to use witness cones to verify that the whole kiln reached the sitter cone range. Link to comment Share on other sites More sharing options...
neilestrick Posted August 21, 2018 Report Share Posted August 21, 2018 If you refire the disks, they'll melt a little more than fresh glaze, but it will give you a pretty good indication of whether or not they'll work at 04. I wouldn't be worried about it being too runny. It looks pretty stiff. Link to comment Share on other sites More sharing options...
Soren Posted August 21, 2018 Author Report Share Posted August 21, 2018 1 hour ago, neilestrick said: If you refire the disks, they'll melt a little more than fresh glaze, but it will give you a pretty good indication of whether or not they'll work at 04. I wouldn't be worried about it being too runny. It looks pretty stiff. Thanks for the advice, Neil. I refired a few items last evening to ^06 to see how this would affect the glaze. I am waiting to see the results tonight after work. Firing twice for glaze is not ideal long-term, though, so I will test this glaze against ^04 firing. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted August 21, 2018 Report Share Posted August 21, 2018 If, after you refire your disks and you discover them to be more bubble-free, you can add a soak hold at the end of your kiln cycle by lifting the weight, turning the kiln back on, and very gently lowering the weight so it doesn't trip. Start your soak at about 10-15 minutes in length, and go from there. You will have to turn off the kiln manually. Link to comment Share on other sites More sharing options...
Soren Posted August 21, 2018 Author Report Share Posted August 21, 2018 2 hours ago, Callie Beller Diesel said: If, after you refire your disks and you discover them to be more bubble-free, you can add a soak hold at the end of your kiln cycle by lifting the weight, turning the kiln back on, and very gently lowering the weight so it doesn't trip. Start your soak at about 10-15 minutes in length, and go from there. You will have to turn off the kiln manually. The soak hold is something I have wanted to try for some glaze firings, since I have had issues where it seems the glaze does not mature completely. I was nervous to try it before, but I may try it now. With the time invested in each ocarina due to precise shaping of the voicing and the specific tuning, I really do not like to have any failures, especially in the final stage after highest anticipation and greatest work input. Soaking will be well worthwhile for my glazed ocarinas if it can eliminate some of my glazing issues. Thanks for the recommendation, Callie. Link to comment Share on other sites More sharing options...
Soren Posted August 22, 2018 Author Report Share Posted August 22, 2018 The re-fire to ^06 did not work to eliminate the bubbles. It seems to have changed nothing about the glaze. Last evening, I re-fired to ^04. Results should be visible this evening after the kiln cools completely. Link to comment Share on other sites More sharing options...
curt Posted August 22, 2018 Report Share Posted August 22, 2018 While you are waiting impatienty for the kiln to cool down, have a read of an extensive thread on bubbles on this forum entitled “Bubble, bubble toil and trouble”. I also have some low-fire bubble pics in my gallery which may be of interest to you. Link to comment Share on other sites More sharing options...
Soren Posted August 22, 2018 Author Report Share Posted August 22, 2018 56 minutes ago, curt said: While you are waiting impatienty for the kiln to cool down, have a read of an extensive thread on bubbles on this forum entitled “Bubble, bubble toil and trouble”. I also have some low-fire bubble pics in my gallery which may be of interest to you. Work seems to help with impatience, as peeking before the kiln is cooled is not an option! Thanks for the references, curt! My bubble issue is certainly not my own! Your pictures and the pictures from the other thread show the same issue and open a whole new area of scientific research for me. Now I will probably make the step into mixing my own glazes, and I have some Ferro Frit 3195 on order. Link to comment Share on other sites More sharing options...
Min Posted August 22, 2018 Report Share Posted August 22, 2018 On 8/21/2018 at 7:21 AM, Soren said: Top left quarter of the disk is with one brushed coat, bottom left quarter is with double coat. It looks like more bubbles in the double layer of glaze when I magnify your image. When you used this glaze before was it on this clay and with the same bisque and glaze firing schedule? On 8/21/2018 at 9:08 AM, Soren said: My test kiln is older and already visually (not functionally) damaged, so I will test in that kiln. Small test kilns can fire very rapidly so results won't be consistent with your other kiln unless you can match the same firing profile. On 8/21/2018 at 7:21 AM, Soren said: There was some hardpan on the bottom, but I stirred the glaze and shook the jar until it seemed evenly mixed. Should I have added a deflocculant to ensure proper mixing and suspension of particles? I would dump out all the glaze from the bottle into another container, use a loop tool or something like that and scrape and cut out any hard panned material stuck to the bottom of the bottle then mix it into the liquid glaze. If it's brushing on okay and not settling out while you are using it (stir it often) then I wouldn't add anything to it for now. I would try thinning it down and brushing on 1, 2, and 3 coats. Laguna recommends using EM2134 over underglazes for lowfire. Makes me wonder if that would be a better choice for over your dark clay. Link to comment Share on other sites More sharing options...
Soren Posted August 23, 2018 Author Report Share Posted August 23, 2018 17 hours ago, Min said: It looks like more bubbles in the double layer of glaze when I magnify your image. When you used this glaze before was it on this clay and with the same bisque and glaze firing schedule? Yes, there are definitely more bubbles in the double layer, which seems to link the bubble issue to thicker application. I think the glaze has lost some water which has thickened it, causing my usual method of brushing to apply a thicker coat this time. This is the first time I am using the clay with stains and oxides, though I have used this clay before. The same bisque and glaze firing schedules were used before, though this is the first time in the current kiln (which is a very similar type to my old kiln, though dial-operated with relays instead of simple element switches of the older kiln). The glaze has never bubbled like this for me before. 17 hours ago, Min said: Small test kilns can fire very rapidly so results won't be consistent with your other kiln unless you can match the same firing profile. I did not communicate this well: my test kiln is very similar to both of my other kilns, both in size and type. The test kiln is just my oldest kiln and the one I did all my learning in (hence noticeable visual damage inside due to dripped glaze and items that fell and glaze-fired to kiln bricks, though function has been fully repaired after my many beginner mistakes). I have not used this kiln since I got my two newer kilns recently, but I intend to test glazing methods in this kiln to avoid damaging the newer kilns. This probably concerns the placement of objects more than firing range/schedule. I may use the old kiln as my glazing kiln to avoid any glaze damage to the newer kilns. 17 hours ago, Min said: I would dump out all the glaze from the bottle into another container, use a loop tool or something like that and scrape and cut out any hard panned material stuck to the bottom of the bottle then mix it into the liquid glaze. If it's brushing on okay and not settling out while you are using it (stir it often) then I wouldn't add anything to it for now. I would try thinning it down and brushing on 1, 2, and 3 coats. Thanks for the tips, Min. I will try this next time. 17 hours ago, Min said: Laguna recommends using EM2134 over underglazes for lowfire. Makes me wonder if that would be a better choice for over your dark clay. I will give this glaze a try. ----------------------------------------------------------------------------------------------------- The results of the ^04 glaze firing were interesting. Most of the test disks resulted with glaze that cleared up and smoothed out better than before, as seen in the examples on the right of the next image. Some tiles got much worse, as seen on the left in the next image, to the point that the bubbles crackle (audibly!) if I touch them. It would seem that the ones that got worse were the ones containing manganese dioxide, so I am assuming that manganese dioxide gases quite a bit, especially at ^04. I think I have read in another thread that this is the case with manganese dioxide. Is it possible that the gases from the manganese dioxide would affect the other tiles in the same firing? I fired all the test disks together for bisque ^04, glaze-fire ^06 ,and re-glaze-fire ^04 (probably around 100 disks ~1" diameter of different colors and concentrations). Double thick coat of glaze still seems to be too thick and is still slightly bubbled on all disks, but the single coat seems to give the results I want. Link to comment Share on other sites More sharing options...
Min Posted August 23, 2018 Report Share Posted August 23, 2018 3 hours ago, Soren said: the ones that got worse were the ones containing manganese dioxide, so I am assuming that manganese dioxide gases quite a bit, especially at ^04. I think I have read in another thread that this is the case with manganese dioxide. Manganese dixoide (MnO2) converts to MnO at 1976F. When that reaction occurs you are going to have off gassing of the extra oxygen. At ^04 you are just coming up to that temperature (depending on firing schedule) which will leave those blisters that you are seeing. 3 hours ago, Soren said: Double thick coat of glaze still seems to be too thick and is still slightly bubbled on all disks, but the single coat seems to give the results I want. Going forward I would measure the specific gravity of your brushing glaze so it will be easier to replicate the correct thickness of glaze. Link to comment Share on other sites More sharing options...
Soren Posted August 23, 2018 Author Report Share Posted August 23, 2018 24 minutes ago, Min said: Manganese dixoide (MnO2) converts to MnO at 1976F. So, should it work to calcine the MnO2 above 1976F to convert it to MnO and make an effective stain that does not off-gas so badly? 25 minutes ago, Min said: Going forward I would measure the specific gravity of your brushing glaze so it will be easier to replicate the correct thickness of glaze. Oh, this is a great help! I knew I could get the same results if I mixed my own glaze by measuring water and ingredient amounts, but I had not considered specific gravity to check already-mixed glazes. I will also be using specific gravity for terra sigillata, so I will start to keep the specific gravity records on glazes as well. Thanks for the help, Min! Link to comment Share on other sites More sharing options...
Min Posted August 23, 2018 Report Share Posted August 23, 2018 23 minutes ago, Soren said: So, should it work to calcine the MnO2 above 1976F to convert it to MnO and make an effective stain that does not off-gas so badly? 51 minutes ago, Min said: Nope, won't work as it is already melting well before that. I would try a stain. Link to comment Share on other sites More sharing options...
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