Cindy Strnad on thu 12 oct 00
Crystalline?Aventurine?
Samantha,
I'm not sure of the answers to many of your questions, however, I recommend
you check out http://digitalfire.com. Look in their educational section for
enough information to keep you reading and absorbing for quite some time.
Not everything you'll ever want to know, but a very good place to start, in
my opinion.
I like Tony Hansen's basic glaze recipe for tan, white, and green, and it's
always worked well for me. I don't like it for cobalt, but that's just my
preference. Some people have found it necessary to calcine half the EPK he
calls for (just fire a pile of EPK in a bisqued bowl next time you bisque
fire) to avoid crawling, but it's not been an issue for me--depends on your
conditions, I expect. You will need to sieve this glaze, as it contains
wollastonite. You'll find the recipe at the site I suggested, along with a
full explanation of why each ingredient is there, and what it does.
As for your commercial glaze that crazes, that's a bit of a problem.
Ideally, you should alter the formula to reduce the expansion, using a glaze
calculation program. As that's not an option, since you don't know the
formula, you might try adding increasing portions of silica and see if that
helps. Start with 5%, and go up from there, maybe in increments of 2% or so.
There will doubtless be other suggestions, and some may very well be better
than mine. It's hard, though, to fix a glaze you don't know anything about.
Hope this helps, and I hope your re-entry into pottery is rewarding and fun
for you.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Dave Finkelnburg on thu 12 oct 00
Crystalline?Aventurine?
Hi Samantha!
Your transparent has a lot of alumina and silica for C6, so it will take
a lot of colorant oxides well before it gets too runny. As a transparent
it may be a little on the stiff side. You'll have to test it.
Yes, the second glaze will be a little on the matt side at C6.
You appear to be taking somewhat the same approach I have--going
everywhere at once! :-) IF it suited you better, you might have less
frustration by making fewer glazes and understanding them better. After 3
years of studying this seriously I have come to the conclusion that firing
is everything and the glaze recipe is just a starting point.
If you are going to Raku, you need some low-fire fluxes. Look for a
boron source at least, such as Ferro Frit 3134, or one of the Gerstley
borate replacements.
I'd invest in a glaze calculation software and learn how it works. You
can predict and produce particular glaze expansions, so you don't have to
have crazing in your alkaline glazes if you don't want that. It's all in
formulating the recipe.
To take the crazing out of your commercial glaze, test adding clay and
silica and do a line blend. Add some to one test batch, mix some plain,
then mix the two together in proportions so you have a line like: 100%A,
80A-20B, 60A-40B,..... and paint them or pour them all on the same tile. I
use a flat tile and prop it up on edge in the kiln so I can see vertical
effects. Label everything with an oxide pencil or paint on some oxide. I
mix RIO w/water, clay for my oxide paint, use a very fine brush. A 30cc or
so syringe from the veterinarian, without needle, is a great way to make the
line blend. You can mix measured volumes fast and accurately.
For all the glaze recipes you can test in two lifetimes, look at
http://www.potters.org/categories.htm
It's the ClayArt archives. Lots of other good stuff there also.
You asked a lot of great questions. I only answered a few. I hope this
helps!
Dave Finkelnburg
Idaho Fire Pottery
dfinkeln@cyberhighway.net
John Hesselberth on thu 12 oct 00
Crystalline?Aventurine?
Welcome back Samantha. Wow, I've never seen so many (I stopped =
counting at 7,469) good questions in one message. I just take a =
crack at a few of them.
Suds Acres Bed & Breakfast wrote:
I've
>been using a bag of some premixed clear glaze from Laguna that crazes on
>my clay which is Laguna's Aspen(^5-6). First Question: What can I do to
>fix this? Add something?
Do you really want to bother? You can probably fix it using the =
techniques Dave recommended, but why? Unless you have an awful lot =
of it on hand it may be more time and trouble than it is worth. =
Especially since you obviously intend to formulate your own in the =
future.
>
>
>Now to get down to business, I am going to get set-up to mix my own
>glazes.
>
>
>I know matt glazes aren't good for dinnerware, but what about satin?
>Semi-gloss? How matt is too matt?
It mostly depends on knife marking. Matt glazes are almost certain =
to do it. Others may. Test them thoroughly for this characteristic =
and make up your own mind.
>
>Also, here is the preliminary list of materials I want to order for
>basic glaze testing and formulation of a few basic glazes, then moving
>on to test and formulate decorative glazes like crystalline glazes. Is
>there something I should have I do not list? Are my proportions way out
>of whack?
>
>
>100 pounds each: Custer Feldspar, Nepheline Syenite, Flint, and Whiting
>50 pounds each: EPK, Kona F-4 Spar
>25 pounds each: Dolomite, Talc, Zinc Oxide, Spodumene
>5 pounds each: Strontium, Bone Ash (watching out for mad cows, of
>course), Cornwall stone, Ferro Frit 3110, Bentonite
>1 pound each: cobalt oxide, copper carbonate, chromium oxide, red iron
>oxide, nickel oxide, rutile, tin oxide, titanium dioxide, zircopax
I would skip 3110 and substitute one that has a good source of boron. =
3124 or 3134. 3110 mainly supplies sodium in insoluble form and you =
have F-4 and neph sy for that
>
>Following are three of the glazes I am looking at for food-safe =
dinnerware:
>Am I on the right track?? How do you use limit charts or whatever you
>call that and where do I find info on that? Silica to Alumina Ratios -
>huh?
I left your glaze recipes below so people can easily refer to them. =
The first one, Transparent 1 does, as Dave pointed out, have plently =
of silica and alumina, but I'm afraid it has too much for good =
melting at cone 6. You have to have enough silica for good =
stability, BUT you also have to melt the glaze during firing. =
Although this glaze has a lot of sodium/potassium and it might melt, =
it also has no boron. It might very well be unstable at cone 6 and =
very stable at cones 8-10. You'll just have to test it to be sure.
Your second recipe (Glossy) does not have enough silica to be stable =
under any circumstances. I personally wouldn't even bother to test =
it.
I can't help but wonder what makes your third recipe (Matt Base 5) =
matt. I fear it is from underfiring. There is not enough alumina, =
magnesia or calcia to get a matt from oversaturation of any of those =
materials. If it is matt from underfiring it will not be stable. If =
that is the case, it might give a pretty good semigloss or gloss at, =
say, cone 7 or 8 or 9.
You will find there are a lot of "garbage" glazes floating arount =
potter-land and, therefore I strongly support Dave's recommendation =
to get a good glaze calc program and learn to use it. You will save =
yourself a lot of time in the long run.
A better glossy base glaze for you to look at might be the one Ron =
Roy used for RR Black. I have shown it below:
Cone: 6
Recipe: Percent
Custer Feldspar 22.00
Whiting 4.00
Talc 5.00
Frit 3134 26.00
EPK 17.00
Flint 26.00
Totals: 100.00 %
Also add:
Bentonite 2.00
Possible Health Hazards:
Talc: wear a NIOSH approved dust mask when handling dry material
Flint: free silica-wear a NIOSH approved dust mask when handling dry =
material
Unity Formula for Ron Roy Black #3 (Custer):
0.097 K2O 0.384 Al2O3 4.120 SiO2
0.209 Na2O 0.333 B2O3 0.004 TiO2
0.547 CaO 0.004 Fe2O3 10.7:1 Si:Al Ratio
0.147 MgO
Percentage Analysis:
66.98 % SiO2
10.59 % Al2O3
6.25 % B2O3
2.46 % K2O
3.52 % Na2O
8.31 % CaO
1.60 % MgO
0.16 % Fe2O3
0.08 % TiO2
This glaze has proven very stable when 2% cobalt carbonate and 9% red =
iron oxide are added to give a glossy black, but I'm not aware that =
it has been tested with other colorant combinations.
And (DUH), I forgot.. which goes in the bucket first, the water or
>the glaze materials? I'm not kidding, and I hope I don't irritate
>anyone, you'd be surprised how long it takes to find this stuff out
>searching through textbooks.
Put water in first, then clay, then the other stuff. If you put =
water, feldspar, neph sy and then clay you are much more likely to =
get concrete on the bottom of the bucket. If you put in the powder =
and then water you will increase you mixing difficulty by 10X.
Good luck on your return to the wonderful world of glazes. John
>
>
>Glaze Name: Transparent 1
>
> cone: 5 - 6
> color:Transparent
> surface:shiny glossy
> firing:Ox or Red
> date: 6/4/96
> recipe:
>
> Nepheline Syenite 56.00
> Whiting 9.00
> Talc 6.00
> Flint 23.00
> EPK 6.00
> Totals: 100.00 %
>
> comments:
> From the NCECA GlazeBase Glaze Recipe Database at SDSU.
> If you find this glaze useful, please consider submitting
> one of your own tested glazes to add to the database.
>
> estimated thermal expansion: 76.32x10-7/=B0C
>
> Unity Formula for Transparent 1:
> 0.102 K2O 0.568 Al2O3 3.989 SiO2
> 0.337 Na2O 7.0:1 Si:Al Ratio
> 0.394 CaO
> 0.167 MgO
>
> Percentage Analysis:
> 67.15 % SiO2
> 16.23 % Al2O3
> 2.69 % K2O
> 5.85 % Na2O
> 6.19 % CaO
> 1.89 % MgO
>
> Talc: wear a NIOSH approved dust mask when handling dry material
>Flint: free silica-wear a NIOSH
> approved dust mask when handling dry material
> Glaze Type: Ca Na . Firing type: Ox or Red. From Val Cushing. VC ed
>
>
>
>Glaze Name: Glossy (Would this be too matt??)
>
> cone: 5 - 6
> color:Opaque White
> surface:Satin
> firing:Ox or Red
> date: 6/4/96
> recipe:
>
> Kona F-4 Spar 19.00
> Custer Feldspar 19.00
> Nepheline Syenite 19.00
> Dolomite 25.00
> Whiting 6.00
> Kaolin 12.00
> Totals: 100.00 %
>
> Also add:
> Tin Oxide 7.50
>
> comments:
> From the NCECA GlazeBase Glaze Recipe Database at SDSU.
> If you find this glaze useful, please consider submitting
> one of your own tested glazes to add to the database.
>
> estimated thermal expansion: x10-7/=B0C
>
> Unity Formula for Glossy:
> 0.091 K2O 0.352 Al2O3 1.630 SiO2
> 0.134 Na2O 0.002 TiO2
> 0.466 CaO 4.6:1 Si:Al Ratio
> 0.309 MgO
>
> Percentage Analysis:
> 51.69 % SiO2
> 18.94 % Al2O3
> 4.52 % K2O
> 4.39 % Na2O
> 13.80 % CaO
> 6.58 % MgO
> 0.08 % TiO2
>
>
> A glossier version of Polished Matt. Glaze Type: Ca Mg AlMatt.
>Firing type: Ox or Red. From Val
> Cushing. VC ed
>
>
>
>
>Glaze Name: Matt Base 5 (Would THIS be too matt??)
>
> cone: 5 - 6
> color:SemiOpaque White
> surface:Satin Matte
> firing:Ox or Red
> date: 6/4/96
> recipe:
>
> Custer Feldspar 40.00
> Ferro frit 3124 9.00
> Talc 9.00
> Whiting 16.00
> EPK 10.00
> Flint 16.00
> Totals: 100.00 %
>
> comments:
> From the NCECA GlazeBase Glaze Recipe Database at SDSU.
> If you find this glaze useful, please consider submitting
> one of your own tested glazes to add to the database.
>
> estimated thermal expansion: x10-7/=B0C
>
> Unity Formula for Matt Base 5:
> 0.136 K2O 0.352 Al2O3 2.982 SiO2
> 0.088 Na2O 0.055 B2O3 8.5:1 Si:Al Ratio
> 0.558 CaO
> 0.218 MgO
>
> Percentage Analysis:
> 64.62 % SiO2
> 12.95 % Al2O3
> 1.38 % B2O3
> 4.62 % K2O
> 1.97 % Na2O
> 11.29 % CaO
> 3.17 % MgO
>
>
> Glaze Type: Ca Mg. Firing type: Ox or Red. From Val Cushing. VC ed
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: =
http://www.frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes =
cannot conceal badly shaped pots..." David Green, Pottery Glazes
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