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Post by Arnie Benton on Feb 2, 2016 16:28:06 GMT -6
I just reread this thread and think that Greg's (Mohawkpiper) post has valuable information. He and I have been differentiating the effects of reduction from the effects of striking - any postfire reduction is a combination of striking and reducing, and many of the effects I had been attributing to reduction actually come from simple striking. Reducing while cooling from the original crystalline firing gives a 'pure' reduction effect.
Peter, I suggest you try it several ways - a post fire reduction at about 1350 F, and reductions while cooling from cone 10 in the high - 1900 - 2000 F range and in the low 1400 - 1300 F range - then you can do the post fire reductions without reducing - and see the effects of striking. My guess is that the group of 3 pieces pictured above is the result of striking in the 1950 down to 1650 range - only the piece on the right seems to have a reduction effect as well.
But, most important, I would try doing your reduction while cooling and not as a post fire - I think you'll get a piece with the coloring of Avi's -
Arnie
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Post by Peter Sorensen on Feb 2, 2016 17:09:24 GMT -6
Hi Arnie
The reduction in a gas kiln is like when learning to ride a bike I had some problem with adjusting the airflow and the damper on the exhaust vent I would like to do the hole glaze firing in the gaskiln but i dont know yet if I have the capability to reach 1276 celcius but i gess that it is the best metode to get a really god reduction in crystalline glaze like Mariscal, to do the hole glaze burn in a gaskiln but if one have to do the next best thing then let the glaze be molten enough to make it able to recheive the reduction with this i mean to make a hold to let the item be saturated with heat so there are a eqrilibrium in the heat in the item and the glaze. but this is just some ideas if the glaze is down cooling from a fire, or if it is heating in a post fire then it must have a hold to reach this eqrilibium before one can compare the burns and I think that Greg is right it is not possibel to alter a high fire reduction with a low fire reduction because the highfire reduction rund deeper than a low fire. but I would like to here your opinnion in this bold assumption, but playe with me, I would like to know what the mekanism is
Peter
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Post by Arnie Benton on Feb 5, 2016 15:35:32 GMT -6
Peter - I like your idea about the glaze melt needed to get reduction, but I don't know if it is accurate. Good reduction can be achieved in a post firing at 1350 degrees F. I don't think the glaze has melted any at that temp. There is something about letting the piece cool to room temp and then heating it up again - don't know what it is - but if you do a 2 hour hold at 1350 degrees in a crystalline firing while cooling, nothing seems to happen. But if you do the same 1350 degree hold in a post fire there are dramatic changes. What's going on??
I found it very difficult to do reduction in a gas kiln at 1350 degrees - I had to increase the gas input so much that the temp would rapidly rise - but maybe that's because I wasn't willing to close the damper as much as necessary because of safety concerns.
Arnie
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Post by Peter Sorensen on Feb 5, 2016 18:13:31 GMT -6
hej Arnie I first have to say I am a novice in reduction and ny trials is limited, the first reduction I did was a copper glaze and the crystal went to a copper color but the back were still a green copper color in first i thougt thati had to to pump a lot of gas in and reduce the oxygen and black smoke come out. of the kiln. the glaze vent mat, but this maybe was becauce i had some barium in it. The next was, that I begun to adjust the burner to a neutral burn and then do the reduction with closing the outvent damper, but as you say then the temperature rises. but then I turn down the gas /flame and read the sensor and close the damper more, i have found that when i am down to 800 celsius I have almost closed the outvent damper, but my kiln is a bit leaky in the lid so i think that this also vent the kiln in it self, I have not worked with copper sins the first time, I mostly have reduced ferro around 1010 celsius is there not a difference for the different oxydes where the optimum reduction temperature layes ? I have noticed that when i get in to reduction in my kiln, there come a blue flame at the outvent, and when the oxygen probe goes down in reading the flame dissapere. gess that any co wil be burned there, but as safety i open all the doore out, when i reduce I dont know wath the optimum atmosphere is as to economic burns
Peter
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Post by mohawkpiper on Feb 5, 2016 20:46:30 GMT -6
Peter,
I did not mean that it is not possible to alter a highfire reduction with a lowfire reduction. I meant that it is not possible (most likely) to alter a postfire highfire reduction with a postfire lowfire reduction, due to the fact that the strike part of the post fire does more than the reduction does (especially in the higher temps), and striking is irreversible, in that a strike higher than the last will have a change (possibly) but a strike lower than the last will not.
You can most definitely alter a highfire reduction with a lowfire reduction IF the first highfire reduction was a direct reduction on the cooling and the second lowfire reduction is a postfire reduction.
And again, this is all assuming you are reducing and striking (or postfire reducing) glazes that have an affect with both or one of reduction or striking.
I also, like Arnie, do not believe the glaze is melting in a postfire at the lower temps. I can remove a glaze catcher and grind the bottom prior to a post fire strike/reduction and the grinding marks look exactly the same after the strike/post fire is finished. If I remove catcher and grind prior to a 2000*F (1093*C) strike or post reduction the glaze definitely softens but it still does not run any. Meaning the grinder marks are gone but the glaze is no closer to the bottom of the pot than it was going in.
Striking does not have to come all the way down to room temp to work either. Though it does have to get close. Where exactly is uncertain to me.
I reduce with alky, not gas, and although I can keep a steady temp with reduction at the lower temps (even 1150*F/620*C) it for some reason seems much more difficult to do reduction at those temps as well like you guys mention. Maybe in a different way, but still more difficult.
G
ps. copper can turn dark in a strike without any reduction in any of the firings. Maybe not red copper colored, but it can still change drastically.
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Post by Koz on Feb 6, 2016 9:25:05 GMT -6
Yo Piper,
Hey I got your special delivery. I was out of town last week.
Send me your e-mail address in a PM so I can get back to you.
Yeah I had it once before but you know how it is.....
Thanks,
Koz
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Post by Peter Sorensen on Feb 6, 2016 18:53:35 GMT -6
Hi Greg Why is you all trying to talk me out to make the reduction at 1010 - 1080 Celsius If it is a copper glaze. it might work, but for a Iron glaze it has to be higher, at least in gold stuff. But againg I have not mutch expirience to back it up. But my teory is that every metal have a melting point and every metaloxydes have a temperature where it can be reduced to the pure metal if the atmosphere is whitout oxygen, Copper oxydes is willing to reduce at a low temperature acording to the pure metals low melting temp Iron needs a higher temperature to melt and and my teory is that high melting metal there the oxydes need a higher reducing temperature than low melting metal ¨this could explane why copper oxydes in glaze easely can reduce in a low temperature . Another teory is whith Iron if you have worked whith tempering steel, then you are familiar with the color chart, and these color is exactly the same color whith can be acompliced with reduction af iron in a high titanium glaze I have worked as a black smith also But work with me am I wrong ? :-) Peter
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Post by Peter Sorensen on Feb 6, 2016 20:58:30 GMT -6
Hi all I know that you all think I am a nut But I wil try to explaine my teori I have alwayes being thought that when anneling a peace of steel then first polish it and take of all the oxydes then heat it to red hot and quench it in hot water or oil then polish it again and then temper it . this is to heat it to it have a specific color. If it if for a spring, then one color,if for a chisel another color the color ranging from black green blue straw and other color when i heat a polished peace of steel it oxydice and the temperatur I heat it to give a specific color ( there the temper chart) my teori is that in a glaze, it is the other way around I have a glaze with a iron oxyde I then reduced it But sins the oxydes is in a glaze I have to have a temperature that is so high that the glaze allow the CO to draw out the oxygen from the Iron oxide it is the other way around if i make a heavy reduction the iron get one color the ultimat, is Iron color as the pure metal. I gess in a glaze it is black. but if the rate of reduction is lower then come the temper color it is the exactly the same just the other way around and the color chard is upside down the hole Idea is the oxydized iron color. when titanium is involved it maybe improve these color changes. Titanium have its own color spectrum on oxydation and maybe it is that that causes the color ( electro oxydation of titanium can make the hole color spectrum). there must be some one out there wit more knodledge to get a good picture lets get a discussion on the mechanic not just from a black smith side :-) Peter
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Post by mohawkpiper on Feb 8, 2016 13:40:03 GMT -6
Koz, PM sent! Hey Peter, In no way was I ever trying to talk you out of reduction in the 1010 to 1080 range. With any glaze. I was just sharing my experience and even mentioned that if you wanted to give it a try go ahead. I can see where you might be coming from with the blacksmith stuff and honestly I don't know if it is related forward or backward. All I know is what I try and what I see from those trials. But iron can most definitely be reduced at lower temps (1300*F/700*C range) So can copper, and so can titanium. I don't think it cannot be reduced at different temps, but you do get different effects at different temps. I think really it has a lot to do with what all is in the glaze, how much, and roughly what temp you reduce at. I feel how hard you reduce has less to do with it. Here are two copper pieces reduced on the cooling at lower temps. These two copper glazes were reduced together. They are very different because of the composition. in lighter or harder reduction at the same temp they look pretty much the same as each other. These three were reduced on the cooling at lower temps. The two on the outside are high in iron, the one in the middle is copper. In a strike afterward they all darken just a little, with the copper one darkening the least. Here we have two iron/titanium glazes (with different frits) reduced on the cooling at lower temps. The glazes are much more white in oxidation, more like a cream color. These two exact pieces postfire reduced (meaning reduced again later) still to the same temp look like this... A glaze with much more titanium and much less iron looks like this from a reduction on the cooling in the same temp range... an iron rich glaze without reduction looks like this... but then post fire reduced at lower temps looks like this... and then postfire reduced again at higher temps, more midrange, looks even darker and more brown. (uglier imo). but iron can change without reduction. here is an iron rich glaze in oxidation. then same glaze struck sure this glaze also has titanium in it. i attribute the change in color in the strike to the iron because tests with varying amounts of titanium only show no changes in a strike. here is a copper glaze in oxidation... then the same piece struck only (NO REDUCTION!) I guess im just trying to say that with a postfire reduction you have to take into the fact that you are striking and reducing at the same time and what you may be attributing to reduction may (or may not) in fact be the cause of a strike, and further testing is needed to find that info out. From testing, striking can change a glaze each time you strike ONLY if you strike above the temp you last struck at. It is additive, not subtractive. If i strike at cone 018, it will have one effect. If i then strike that same piece to cone 015 it will look different. If i strike it straight to cone 015 it will look the same as being struck first to cone 018 then to cone 015. If i strike a piece to cone 015 then strike it again to cone 018 the second strike to cone 018 has no effect and it just looks like it was struck at cone 015. So a postfire reduction at a higher temp, then again at a lower temp will most likely not have any effect the second time around at a lower temp. G
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Kuba
Full Member
SztukKilka in Old Formu
Posts: 111
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Post by Kuba on Feb 8, 2016 13:48:26 GMT -6
One questions. What is maximum number you did strike firing to one piece? P.S. Very interesting results, I need to investigate is because I also think that striking giving more dramatic changes that I supposed in the past.
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Post by Peter Sorensen on Feb 8, 2016 17:49:41 GMT -6
Hi Greg , Kuba and all I am not fluent in the English langues so I am not familliar with the term Striking is it the fact discribed by Bill boyd ? that one can alter a glaze fired in oxydation by fired it a second time in oxydation. is this wath you mean with strikink ? I ask as a stupid I know. if you can tell what the strikingis in a Kiss term I will be glad. and then I will be elaborating my thoughts but I can say my ideas is not som fact just an ideea. blacksmith or not, every discovery come out of an idear but as you say not all idear is worth working on, but tell me what striking is and I vil try to make my Idea clear.
Peter
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Post by mohawkpiper on Feb 8, 2016 18:17:25 GMT -6
Kuba, I used to strike to a temp, but have found that it is more accurate to strike to a cone. Before I was using cones in my strikes, I struck once to ~2192*F (1200*C) trying something else entirely. For the glaze I used then (a cobalt glaze) there was no effect on the color really though the bg turned a sort of weird matte finish in areas and the crystals sort of disintegrated. I cannot find my pictures from that one in particular so I have nothing to show from it. Apart from that I have struck to ~2000*F (1093*C) and a yellow Iron glaze turned a pearly white. A reduced titanium glaze turned a sort of metallic titanium white.
I don't normally go that high, usually around cone 018.
Peter, yes a strike is just reheating in oxidation in a second firing. It is not stupid to ask. I do not know what it would be in KISS terms.
Any idea is worth working on or pursuing.
G
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Post by Peter Sorensen on Feb 8, 2016 19:25:35 GMT -6
Hi greg Just to adjust the blacksmith thing I have done a lot of thing in my life and once it was smithing of the metal, you name it. here is an example from my silver period. but I will come back when i have an answer on my thought on the iron oxydation / reduction it take a little time for me to translate my scribelings Peter
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Post by tileman2 on Feb 8, 2016 23:21:55 GMT -6
Beautiful, beautiful work gentlemen. Tom
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Post by Arnie Benton on Feb 9, 2016 10:25:42 GMT -6
Here are examples of glazed pieces that were struck at 1850 degrees F - heated from room temp, held for about 15 minutes at 1850 - I'm showing what happens when you just heat a glazed piece, with no reduction. Before - After - Second piece - Before - Then postfire reduced at 1350 F - Then struck at 1850 F - Both pieces start with the same glaze - Ru 5 IL 3 on the bottom and Cu 1 Co .5 Fe .2 on top. What's clear, at least to me, is that just heating to 1850 degrees causes major changes. This fact has to be considered when evaluating the effects of post fire reducing at a high temperature. Also, when a previously reduced piece is heated to 1850 degrees the piece reoxidizes but the result is very different than if it hadn't been reduced. Compare the first piece with the second. I can't explain any of this. But it does show that reducing while doing a crystalline glazing is very different from reducing in a separate firing. Arnie
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