High Bridge Pottery

I am not sure why a kiln would trip it as they work by comparing the power going in and out and if they don't match then it cuts the power. In the UK most panels have a GFCI (RCD) that all the power has to go through first before any breakers. Seems better to have one as if current starts flowing through you to ground then it will probably save your life.

Yea, I would try a firing to only 100c first and figure out what's what. Something like 100c top temp, pot F1 set to 5, t.F1 set to 30 min and t.F3 set to 10 min and see what happens.

The confusing bit seems to be the pot F1 (%). As you can only set the top temperature I am guessing pot F1 (%) tells it what percentage of the top temperature to go to and t.F1 tells it how long to take. F2 just seems to be a full power ramp up to the top temperature as you can't set it anywhere and t.F3 is the hold minutes at top temperature. I can't figure out what else pot F1 would mean. An example of how I feel it works would be you set top temp to 1000c and pot F1 to 6 and t.F1 set to 6.00 or however many hours and it should go to 600c in 6 hours then full power to 1000c.

I might have to look into making rubber master molds but it is just another process to learn so I am trying to avoid it. I have no problem with the FDM surface having striations. Going to try some full size prints as these have been 25% / 37.5% the actual size I want while I tested mold release.

I don't think there's any undercuts as some places it sticks and others come out well. Big chunks left in with PTFE spray as it was hard to apply evenly across the form. Here's a bigger photo of the mold, to me there's some clean edges and other ones that didn't release properly. I don't mind the texture but I think after shrinking 10% and being glazed it will be difficult to notice.

That's pretty much the technique I used with soft soap/mould makers size for the first photo, it does work pretty well and I am sure my application can improve. I also tried using a PTFE dry spray yesterday but had worse and better results as it's tough to get an even covering.

I did try using soft soap which is a "non-hazardous composition of potassium soap and vegetable oil" and I think similar to Murphy's Oil Soap. I was letting it dry completely before pouring in plaster so maybe I should pour before it dries. I have ordered some PTFE/Teflon spray to see if that works any better.

Thanks Peter, I wonder what plastic they are using, maybe PETG as they don't seem apply anything to help the plaster release. I have done some printing with PETG but it's not as easy to print with as PLA.

I have been 3D printing some forms to cast in plaster but found it time consuming setting up cottle boards every time I wanted a new mold. Started working on getting a form that I could pour plaster directly into to make the mold. They turned out quite good, I just need to find the right release agent to use, tried a beeswax polish and soft soap but neither seem to work as well as I would like. Going to buy some proper mold release or other spray that will let the plaster release nicely but my initial tests are promising If anybody knows a good product I could use as a release agent please let me know, using PLA to print.

It's a lot easier to use a thicker gauge wire for two elements in series as the resistance for each element is about 4x lower. I also think if you lose 1 out of 2 elements you may as well have the kiln turn off because it probably won't finish firing with 50% power.

Instead of having a live and neutral running to the start/end of each element with jumper wires you will run the live wire to the top connector and neutral to the very bottom connector and then just use the element tail from one element to join the middle connectors. You could use a wire in the middle but the element tail will probably be long enough.

You can run 20 amps through a 13 amp (British Standard 1362) fuse without it blowing out. My Cromartie HobbyTech 40 litre draws about 2.9kw/12 amps through a 13 amp plug fuse without any problems or excessive heat generation. For a 2.5kw kiln I would still change from parallel elements (46 ohms per element) to series (11.5 ohms per element) as they will use a thicker wire giving better element life. I know Cromartie advise that on all their 40 litre kilns and it seems sensible to do it here too.

You can run up to 3kw through a 13 amp fuse no problem. Those elements are wired in parallel so you need to use 1/RTotal = 1/R1 + 1/R2 If I assume the bottom element has the same ohms as the top 52 ohms you measured it comes out to 26 ohms (2.2kw) for RTotal so it seems like they may have upgraded the elements to draw 2.5kw. You will be better off switching from parallel to series elements as then they can use thicker wire and the elements should last longer. I do agree if you order a 2kw set they will probably be worse than what you have now.

Not sure if this is the same as murphy's oil soap but "Potter's Soap (potassium oleate) reacts with the plaster (calcium sulphate) to form calcium oleate, or a 'soap scum'. The 'scum' that forms on the surface creates a nonporous waxy film, sealing the plaster." - https://www.artcoinc.com/potterssoap.php#potters No idea if that means you can't wash it off either.

Yea they are saying to use 3.5g for every 1000g of dry material but I haven't found that to get anywhere near fluid enough and I am using double that at 7g for every 1000g of dry material.

Are you buying in the clay? I wouldn't think there's much price difference if you are making it up from raw materials? I was actually doing some tests yesterday to try and get 1.8sg, it has been pretty easy to get to 1.7sg with: 1000g Dry Material : 430g Water : 3g Sodium Silicate (140s) : 0.1g Soda Ash Yesterday I tried 1000g Dry Material : 400g Water : 7g Sodium Silicate (140s) : 0.1g Soda Ash (It was 1.75sg after initial mixing but 1.8sg this morning which is a little odd. Probably a measuring error on my part) 1000g Dry Material : 375 Water : 5g Sodium Silicate (140s): 1g Soda Ash (1.8sg after initial mixing and still 1.8sg this morning) They are slightly more viscous than I would like and I have read that going over 0.3% Sodium Silicate is not great for mold life but they cast fine this morning and poured out easily after 20min in the mold. My clay recipe is Hymod AT Ball Clay - 60 Nepheline Syenite - 30 Petalite - 5 Alkaline Frit - 5 Not exactly stoneware as it is fired to cone04. I ran out of Neph otherwise I would do more tests. Thought about using soda feldspar instead as it should act the same with my deflocculation tests?

That is great Good that you happened to have the right rod! I just guessed that they looked like a 5mm diameter. What size rod did you use in the end?

@Callie Beller Diesel You could write it out as: dry weight = portion weight / total weight x batch weight You could either work it out per bucket of slip or make sure to take the dry weight off the batch weight for next time you work it out. Using Callie's example ~ 1500 / 7500 x 5000 = 1000 if you wanted to keep working it out every time you need to take off the 1000 of dry weight from the batch weight for next time so it would be 1500 / 6000 x 4000 = 1000 (assuming you haven't lost water to evaporation) If the slip is thin enough to measure the volume accurately you can weigh a volume of slip and then (volume of slip weight - same volume of water weight) x 5/3 = dry weight If you can measure the specific gravity and know what dry weight you need you can also work out what volume of slip you want with volume needed = (3 x dry weight) / ((5 x specific gravity) -5)

I was just pondering if you could still get a positive test without actually firing any lead based glazes in the kiln due to trace amounts in other materials. Would be interesting to see if you could get a positive test on a kiln you know hasn't had any lead in.

Sounds pretty dodgy, I don't know much about USA plugs but had a quick wiki read and the 10 plugs seem to say they have been phased out as they are not grounded? I will let somebody else who know more answer but there's really no need to cut off a brand new kiln plug. Make image smaller: if you go to https://cloudconvert.com click 'select file' and choose the image you want to resize change the 'convert to' dropdown so that you have jpeg selected click the spanner icon and find where it says 'Quality' and input 60 into the box then click ok Now click convert and download your image, if it is still too big reduce the number you enter into the quality box.

If you put a cone04 in a cone5 firing you will probably end up with it sticking to the shelf unless you are making a cone pack with a bit to catch the melted cones in. Turned out useful for problem solving this time but I wouldn't normally include an 04 unless you make something to catch the melting cone that's not your shelves.

How much lead do these tests pick up? I thought most ceramic materials are contaminated with trace lead, sure I remember Neil talking about an old job where he would test (maybe zinc or tin oxide) for lead contamination.

Not sure if this option is on phones but on my desktop if you right-click you have "paste" and "paste as plain text". The plain text option will remove all the colour and size formatting and get you back to the normal forum font style and colour.

It sounds like you are saying the 04 firing cones are not right but they sound bent the right amount to me. Are you sure you did a cone5 firing and not cone05 as having the 04 start to bend sounds like you did cone05 by mistake.

I think it's just an optical illusion making them look like craters. If you look at the rim in the lower right the light source is also coming from that direction and the rim is casting a shadow onto the plate. They don't particularly look like blisters to me. I am guessing you would have noticed all the bumps when glazing if it was some chunks in the glaze but worth sieving through 120mesh just to make sure. Maybe you caught a kiln brick putting a shelf in and knocked some debris onto the ware? You could try sanding them, might give you an idea if they are solid chunks or filled with air?