High Bridge Pottery
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Posts posted by High Bridge Pottery
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1 hour ago, KellySnider said:
I check the cones and all 3 are curved over with just the tips touching the shelves - I know they should be at 90 degrees....
I thought I would try the cone 5 with some test tiles I had glazed...Those cones never even budged. I put an 04, a 5 and a 6 - the 04 bent slightly (maybe 1/4" and the 5 and 6 didn't bend at all, just turned white.
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.
- Babs, KellySnider and Hulk
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1 hour ago, Hulk said:
looks like concave pits to me, particularly the lower right one
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?
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When my cones have been at the 1 o'clock position or 'just starting' I find a 15-20 minute hold will do the job.
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It looks like the Rohde uses 1 long element over 4 grooves and the Nabertherm uses 3 elements over 6 groves. Never seen a design with 1 long element like that before.
I just mentioned elements because they are a consumable and don't last forever so will need replacing at some point. I wouldn't worry too much about the customer service, if the kiln arrives broken I would guess you are dealing with HotClay not the kiln manufacturer.
Rohde
Nabertherm
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From a quick search it looks like the Rohde elements are about £100 cheaper too. I think I got the right models of kilns. Can't seem to spot what kind of thermocouple the Rohde is using but I would guess it's the same typeS as the Nabertherm.
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That's how it looks for me, not sure how the layout is for non-desktop users.
I agree with JohnnyK that the old list of topics with new posts was better than the new recent posts list.
Here's what is used to be using wayback machine.
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I could certainly get by with a 4 segment program and £400~ extra just for more segments seems like a rip off unless it has more extra features.
My typical bisque would be 200c per hour to 100c then hold at 100c for 30 min. 150c per hour to 1000c then hold at 1000c for 20 min which would be the 4 segments.
A glaze firing doesn't really need the first hold so for a cone 10 firing it would be 250c per hour to 1180c then 60c per hour to 1280c and a 20 min hold at 1280c. You don't have to hold at the end but they can help to even out the temperature in the kiln. You would change the last ramp segment depending on which cone you want as cones are specified as a rate of climb (either 60c per hour or 150c per hour) for the last 100c of firing to a certain temperature.
250c per hour to 1180c may be too much for thick work or large platters and end up cracking them so something like 100-150c per hour would be better.
You could even add a controlled cool to the glaze firing as my example above is only 3 segments. Cooling slower than just turning the kiln off is good for crystal growth, if you are looking to get into proper crystaline glazes then I would probably go with the 20 segment. Not something I have tried myself but I have read they need very particular firing profiles on the way up and down to get big crystals.
In the end it all depends on how you like to fire. More segments will give you more ways to try and solve issues with your clay and glazes but from my experience you never need the firings to be overly complicated with different ramp rates and holds.
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In my recent glaze tests I have found 20% kaolin 80% frit will suspend really well for at least a few weeks to a month whereas 10% kaolin 90% frit will be trying to hard pan in about 12 hours.
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It looks like holds are their own segments so you won't be able to get very complicated with the firings. Say you had some thick work and wanted to heat to 80c and hold for a few hours that would be two segments. One going from 0c-80c in 30 min and another segment holding 80c for 2 hours. Then you only have two segments left for the rest of the firing (which is possible)
Some people like to heat slower through quartz inversion (575c I think) or do a hold at top temperature or even a slow cool. You could do a bisque firing in 1 segment if it was 0c-1000c for 10 hours (100c per hour) but if you wanted to go 0-80c for 30 min, 80c hold for 2 hours, 80-550c for 3 hours, 550-600c for 40 min, 600c-1260c for 4.5 hours, 1260c hold for 20 min you are looking at 6 segments. It really depends how complicated you want to get. A glaze firing could be 1 segments with 0-1260c for 8.5 hours and done.
Not sure I explained the best
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9 hours ago, cwells said:
I'm so confused by that with its melting point being so high. Guess that comes with being new, can't understand everything at once. Thanks!
It's the same way Silica doesn't melt until 1700c by itself but by having a mixture of oxides you end up with a lower melting point.
A good example is a mix of Silica and Alumina. "The melting point of silica is 1710c and that of alumina is 2050c. At the eutectic point, when 10% alumina and 90% silica are mixed, the melting point is only 1545c. All other ratios of silica and alumina have higher melting points."
https://lindabloomfield.co.uk/wp-content/uploads/2017/04/Bloomfield_May17CM.pdf
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FeO is certainly a much more powerful flux but Fe2O3 can help with melting. I don't think you are missing anything entirely, there's quite a fine line/small area of chemistry that will make a good matte glaze as you have found out by removing the iron oxide.
All the B2O3 Fe2O3 Al2O3 oxides are a bit weird and can act as fluxes and stabilisers. Can be called intermediate oxides or amphoteric oxides.
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Dunno if it would work but you could put them in a box with an ozone generator, just be careful not to breathe the O3.
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Made up a 1kg batch with 1% bentonite added to see what it's like to throw with. Very rusty on my throwing so left it quite soft to make it easier. I tried a bowl first but that ended up flopping down so I put that on a plaster batt to dry out some more. First cylinder on the right was with the same really soft clay and the left one is the rewedged bowl. Seemed to throw about as well as the cone10 clay I used to work with. Might try another 1kg batch without the added bentonite and see if I can notice much difference. Can't find my good wood tool for cutting in the base
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That's true you could make them all 1.44 ohms instead on 240v and get 16.6amps and a 4kw kiln instead of 15 amps and 3.6kw. Looks like the controller has a 30amp relay so that shouldn't be a problem on the relay either and give you additional room for wear.
What size is the breaker on the kiln? 16.6amps +25% does just take you over 20 amps but it might be bigger anyway.
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They are definitely worn out, you need to get new ones made up with a resistance of 1.6 ohms per element. They will have been that resistance to start with but over time they wear out and increase their resistance.
It's not that you can't supply enough power to the kiln it is just that as they wear the resistance increases and the amps will decrease meaning you are getting less power to the kiln. Amps are just a function of voltage divided by resistance, we can't change how much voltage comes in the wires so by changing the resistance you can increase how many amps the kiln will draw. It's one of the reasons we have breakers and fuses because things can go wrong and many more amps can be supplied through wires not rated to handle that power if the resistance drops for some reason like a short circuit.
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I always found it pretty tricky to get an accurate reading from long lengths of wire as it liked to coil back onto itself and give weird readings by shorting out sections. Measuring the length with a stick cut to 1 meter and adding 5-10cm extra for the tails seemed to work pretty well. Wearing safety glasses is a good choice when measuring and winding as it likes to spring back and swing for your eyes.
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Thank you for sharing. Doing the maths and either pretending the water doesn't exist in the weight after dipping or assuming the bisque weight it the same as fired clay weight and LOI is 6.5% you are somewhere in between 5-10% dry glaze for the weight of bisque. I always felt it would be 1% or less but never ran any tests to prove that to myself before now. I think for a glaze that could be thinner maybe 3% is the lower limit.
- Callie Beller Diesel and Min
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Ok think I got it right this time and didn't confuse my metric and imperial. 12 gauge comes out a bit under the 5-7 length but I wouldn't worry as it is in the 2-3 stretch length.
12 awg - 0.1340 ohm per foot, 2.052mm diameter.
d = 0.002052m
D = 0.007052m8 / 0.1340 = 18.197m (59.7f)
18.197 / (0.007052 x pi) = 821 turns
821 x 0.002052 = 1.685m (5.53f) wound lengthLooking at 13 awg you can probably just get away with stretching it a bit further than recommended.
13 awg - 0.1690 ohm per foot, 1.8288mm diameter
d = 0.0018288m
D = 0.0068288m8 / 0.1690 = 14.429m (47.34f)
14.429 / (0.0068288 x pi) = 673
673 x 0.0018288 = 1.231m (4.04f) -
You are right, sorry about that. I also noticed in the video he is adding the wire thickness to get the D value so I will rerun the calculations and not mix up feet and meters!
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16 awg might work if D is 5mm, couldn't find any exact numbers on what the internal diameter is but they look about 5mm. Can you post what the internal diameter is?
8 / 0.3388 = 23.613m
23.613 / (0.005 x Pi) = 1503 windings
1503 x 0.001291 = 1.94 meter (6.36 feet) length unstretched which you can stretch to 15 feet and is within the 2-3 stretch ratio
4.57 meter (15 feet) x 5 = 22.85 meter so under the 23.613 length of straight wire.
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38 minutes ago, elenab said:
If my math is not wrong, can the new coil go around the kiln only once instead of 3 times? But I believe something is wrong with my math, it can't be that ( for the same amount of ohms) the longer the wire the thicker it is.
Thicker wire has less resistance per ft so for the same resistance you will need a longer piece of thicker wire to get the same resistance as thinner wire. Not sure that you need 5-7x longer than the coil length as it depends what sized rod you are winding it around and what gauge wire you are using. I would just measure what gauge you have in the kiln now and go with something similar. If you need to stretch it to 15 feet then then it's probably going to be around 5 feet before you stretch it and need a mandrel (rod) at least that size and matches what internal diameter you need for the coil.
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Once it's neutralised with bicarb isn't it fine to pour down the sink as it's just salty water?
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1 hour ago, Callie Beller Diesel said:
When I used the Brongniart calculator to figure out the dry weight of 10 ml of a glaze with sg 1.4, I got 4.6g.
This one? https://pietermostert.github.io/SG_calc/html/brongniart.html it gives me 6.5g as the answer. If it's a sg of 1.4 then 10ml should weigh 14g? and 10ml of water is 10g? I use the post on clay art so (14-10) x 5/3 = 6.667 Unless I am wrong about the glaze weighing 14g.
I tested the glazed bisque again this afternoon and got 7.25% of bisque weight for a 2 second dip and 14.75% for the 6 second dip. Some off the loss from my previous value in % of the 6 second may be from touching it and a bit of water as my glaze is a little dusty on the surface and comes off easily.
I would be interested if anybody wants to try out weighing bisque then glazing and drying to see what values they get.
Finally got some HCl to try dissolving these crystals, just got to work out how to dry and weigh again after sitting in HCl as I am assuming it wont all dissolve. Need to read about safety and disposal, guess I should neutralise it before disposal and figure out a way to catch the crystals again. I don't want to ruin the mesh in my sieve so maybe coffee filter paper.
Necessary to Seal Underglazed Surfaces?
in Clay and Glaze Chemistry
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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.