Sunday, June 13, 2010

Crystal Glaze Tests

The working area of my studio is quite small, so when I test glazes my wheel tends to double as a table, and a temporary bench is made from an old desk and a couple of boards. It is very snug!

In my last post I showed a couple of photos of glaze tests I had tried with new glaze bases. I thought that you might find the next stage of testing quite interesting (I do!!).

The base recipes (which give the white glazes) come from a "how to" section on Jesse Wiseman Hull's website, which should be a "must read" for anyone embarking in crystal glazing (I forgot to mention this one to Carlie Star in my reply to her comment on my last post).

Anyway here is the first one:

Ferro Frit 3110 or Fusion Frit 75: 51%
Calcined Zinc Oxide: 25%
325mesh Silicon Dioxide: 24%
Titanium Dioxide: 6%
CMC: 1-2%

I use frit 4110, which is the way 3110 is numbered in this part of the world. I did not use CMC , but added 1 percent bentonite to assist glaze suspension and application. I am firing to the point where cone 9 is just starting to bend. The clay I use for my pots does have quite a fluxing effect on the glazes that are over it, so other clays may demand a higher top temperature. I have done a 3 hour soak at 1100 centigrade to grow the crystals as the kiln was cooling down.

Here is the base glaze.

Base plus 0.5 cobalt carbonate & 1.0 copper carbonate.

Notice that the crystals are large (up to 50mm) and have very distinct borders. As was expected from crystal glazes I have made with other bases, the copper coloured the background, and the cobalt tends to gather in the crystal.

Base plus 4.0 Red Iron Oxide.

The crystals are much smaller, and have blurry margins. There are nice light flecks in the background and crystal areas of this glaze.

Base plus 3.0 Red Iron Oxide & 1.0 cobalt carbonate.

The addition of cobalt has made the background and crystal colours richer. The crystals are larger, are almost matte, and are a grape-like purple.

Base plus 1.0 Red Iron Oxide & 1.0 cobalt carbonate & 1.0 copper carbonate.

Equal amounts of iron, cobalt, and copper do show three colours. The crystals have packed together with rather too much enthusiasm for much of the iron coloured background to show through, a slight adjustment of glaze thickness, top temperature, or a decrease in the amount of titanium in the glaze may sort this. I will also play with increasing either the copper or the cobalt to give more contrast between the blue and green colours.

Base plus 5.0 manganese dioxide

I had some difficulty applying this glaze. My first sin was to make it too runny, the second problem was that the addition of manganese tended to make the glaze want to form a hard lump in the bottom of the glaze bucket. The glaze is not all that nice colour wise at the moment, but is very interesting and complex when closely examined. The crystals have dark centers, and the most obvious crystal structures are surrounded by pale areas that extend a long way. I will play further with this one!

Base plus 4.0 black nickel oxide

I am not having much luck with nickel on its own. I have tried it before with other bases with much the same result! This grew a very small crystal or two. I'll try again with just 1.0 percent nickel and see what happens.

No snow last night, and some sunshine here!!! Much better day than forecast by the met people.

Must dash now. Kiln to unload with some bisqued work.


Tracey Broome said...

You are enjoying this way too much, I think you must have been a chemist in a previous life. What a fascinating process, boggles the mind!They are really beautiful though aren't they

Linda Starr said...

Oh I like the white on white almost like purity itself. What do you do with all those runs, you must have a terrible time grinding all that off? Your testing is amazing. the last olive green is an ususual color.

Armelle said...

I like the white & ivory too, and base plus 3.0 red iron oxyde and 1.0 cobalt carbonate is amazing. This ferro frit 3110 makes a satin texture. When I tried to do my tests, I enjoyed this frit you recommanded me, melt with zircon, a beautiful white.
May I say you , happy Matariki ?

Hi from He of the black feet to She of the pink ones, today he was fiting with a young Ginger, our neighbor!!!
Best wishes to you, Laura and Ginger

Peter said...

Hi Tracey,
I think I enjoy having my mind "boggled"!! Due mostly to being woken up by the neighbour's dog howling in the chilly night, poor thing..., I was reading some of Frank Hamer's Potters Dictionary last night at 3am about Valency ("the theoretical combining power of the atom" FH) and Double layer theory ("which explains the electrostatic charges on colloidal clay particles whereby particles repel one another..." FH). The things we do!! I am afraid my brain is mostly mush, however, lots of good ideas started, and then they hit an area of marshmallow! The crystal glazes are amazing though, they do make opening the kiln like opening a gift from an eccentric relative who sometimes gives you something beautiful, but other times the contents of the parcel scares you!

Hi Linda,
The grinding off of crystal glaze runs is not my most favorite occupation, but it is part of the package really! I do the rough part of it with a bench grinder, and finish off with a hand held tool that is more what a model engineer would use (or a mad dentist!!).
The nickel glaze with the olive green is fairly horrid at this stage, and behaves very badly. I did something interesting with a nickel glaze that was as bad as that in the series of crystal glazes I did for the exhibition. I found that the nickel glaze over a manganese glaze could do lovely things, even making yellow (just once!!).

Tena Koe (Greetings) Armelle,
Ka pai (well done!), Nga mihi o te Tau Hou! (Happy New Year!).

I look forward to trying the new crystal glazes on some pots now, I think that the two that you mentioned will be really good. The same frit is good for raku too! Amazing really!

Ginger is fast asleep in front of the electric heater. She of the pink feet is outside at the moment. It looks like it might snow later today. She of the pink feet has not seen snow yet, so it could be fun!

Nga mihi nui (with best wishes)

P, L, G & NS

Linda Starr said...

The illusive yellow, I hope you find the secret, a pale yellow with crystals - wouldn't that be something.

Pat - Arkansas said...

The white "base coat" took my breath away! What amazing things happen to minerals and chemicals when just the right amount of heat is applied!

As another commenter stated, you are having way too much fun! Good! I love the results.

Have seen some interesting/fascinating documentaries on TV lately that featured NZ South Island birds and wild life. It's a wondrous place in which you live!

Peter said...

Yes Linda, Yellow... It would be really great to get it sorted. I feel like an alchemist, trying to make gold from sulpher and mercury!

Hello Pat, Apparently the zinc and silica combine in the kiln to make an artificial version of Willemite (Zn2SiO4), which is a naturally occurring mineral. According to the wonderful Wikipedia, Willemite is a highly fluorescent green under shortwave ultraviolet light. It would be fun to see if crystal glazed pots turned green under similar lighting!!

How nice that you have had documentaries about NZ South Island birds on your TV. They were probably made by The Natural History Unit, which is based in Dunedin. Sadly, such is the poor state of TV in NZ, we rarely get to see wildlife documentaries here, and the ones that the Unit make are almost all screened offshore!! We do see reruns of Friends here, American Idol, and The Simpsons (which makes for an intriguing cross cultural exchange!).

jim said...

lots of info there... i wish i had the patience. love the large crystals on the second one down. i know there's not much going on crystal-wise on the black nickel oxide one but i really love that hue of green.

Peter said...

Hi Jim,
Really nice to hear from you. I guess that it might be possible to get that nickel green in a glaze base that doesn't run so much. It certainly is an unusual colour, and there is an interesting fleck through it that is probably the result of the titanium content of the glaze base. I don't know if nickel needs a largish quantity of zinc to be in the glaze base to produce that sort of green, or if it will do it anyway at 4 percent. It is a very strange metal that is also capable of producing pink and blue! If you haven't already done it, you might like to try some nickel in one of your glaze bases and see what happens!
The only thing I don't like about nickel is its toxicity. It is very nasty and needs to be used with gloves, masks, and care as it is a known carcinogen. Still, the best things in life often have some risk!

Angie said...

I love the base glaze with all the crystals . Not being a potter I am not sure whether you put a second glaze on and that is what the other effects are.... or you mix the chemicals with the base to create the new finishes. I love the last colour you achieved but wish there were crystals to see and my other fave is certainly the base coat. take care xx

Peter said...

Hello Angie,
Lovely to hear from you. I can see that I will have to do some more work on that last glaze, and see if I can make it grow crystals more successfully!

A base glaze is a bit like a very plain cake recipe, that has flour, eggs, baking powder, and sugar. It will make a cake, but a very basic one. If you add cherries to the cake recipe, you have a cherry cake! Or some mixed fruit might turn it into a fruit cake.

Glaze base recipes are quite similar to that. On their own the glaze base recipe will make a glaze of some sort, and possibly quite a nice one, but this can also be turned into something else just by adding another ingredient, such as cobalt carbonate, (which will probably make the glaze blue), or some copper carbonate (which might make the glaze green).

When testing glazes, it is quite useful to make a largish quantity of a glaze base, and then test measured amounts of it with different extra ingredients added. It saves quite a lot of time in glaze preparation working this way, and is also likely to have greater accuracy.

Big hugs,P xx

Angie said...

Thanks for the excellent explanation ... this means that each potter is a sort of inventor, as his final perfected glaze will be different from any other potters ...Yeah ... that makes you an inventor ... a chemist...and a potter....take a bow sir. lol

Peter said...

Thanks Angie,
The potter as an "inventor" is well put! There is always something more to understand and discover about the process, or the materials that we use, and this need to look, to think, and to test things makes life more enjoyable, and the world more marvelous!

lancelott said...

not to use nickel-titanium, or ugly green leaves, best single nickel, crystal blue and the background will be ambe

Anonymous said...

Started also to play with cristal glazes and did find one basic with 3110, zinkoxide and silica. added nikkeloxide and it turns green (olive) background with large blue crystals. could not believe and did again, same result.

Anonymous said...

I have been trying less than 1% nickle in a titanium crystalline glaze, more seems to result in that green.
What type of clay are you using?

Peter said...

Hi Roz,
Good to hear from you. Not sure if you are asking me, or the other "Anonymous" about clay, but, I use Abbots White for my crystalline glazed pots. It is a mid fire white that is at its top limit at about cone 9. P.

Arlette said...

Hi Peter, the base glaze , first picture is with the titanium or without titanium ? What is CNC ? I'm actually looking for a crystal glaze, white background and white crystals, so this one comes nearby I think . Thanks, greetings from Belgium, Arlette

Peter said...

Hi Arlette,
Good to hear from you, and welcome to my blog. (I also received the Email from you with the glaze photo, and will email you with more information about that.)

The first picture is of the base glaze with the addition of 6 percent titanium dioxide. The titanium does improve the crystal growth and shape, and it also makes the glaze surrounding the crystals more opaque. For an interesting variation on this, you can use rutile in place of titanium. This will give a "softer" looking crystal with more creamy colouring.

CMC is a type of gum that some potters add to the glaze to make glaze easier to use, especially glazes that have a large frit component and little or no clay. It helps prevent all the glaze materials settling rapidly to the bottom of a bucket that is full of liquid glaze and forming a lump!
More information about CMC is available on line, I found that has useful information

Bentonite can be used in place of CMC gum, as it also can aid glaze suspension.