The Thicker, The Glossier
Stands to reason that larger/thicker pieces have a Glossier finish, than smaller ones. Does it not? A thicker piece takes longer to dry, yes? With longer drying time more salts wicks through to the surface, agree? The more salts on the surface the thicker the glaze forms, right?The two figures in the image here are constructed from the exact same clay/Egyptian paste mix. They dried next to each other; they were fired along side one another in the kiln. Mason stain, pansy purple, was added to the basic mix, 2.5% by weight. You can observe here that the thicker the glaze the bluer it appears. On the bottoms where no evaporation occurs their color appears identical.
Lots of cracks developed in bigger pieces as they dried. Possibly, the introduction of sand or grog would alleviate this cracking. Of course additions to the basic recipe might also affect the color. The addition of grog would also improve this clay's ability to stand up. There’s always more experimentation to be done.
posted by anitra @ 11:19 PM
6 Comments:
HI I find that really interesting the difference between the 2 figures and the amount of gloss/glaze. I work with EP and make beads - I have been having numerous problems of late and have slowly been discovering the useful effects of salt and how it effects the firing of the beads.
Do you think over time there is the chance the salt will leach out or bloom on the surface of the beads in any way? Salt is used in ceramics so much I would figure it is fairly stable once fired? If you are interested in my work
www.kriketdesigns.com
www.kriketbroadhurst.blogspot.com
Hello Kriket,
Salt, as in salt glazing, is very stable, because the salt completely disassociates in the stoneware temperature range. That is because soda is volatile at temperatures above 1200°C (2100°F). However with Egyptian paste the temperatures are not that high, it's in the earthenware range, 850°C to 1000°C (1550°F to 1800°F). Salt forming on the surface suggests that efflorescence is still taking place after firing.
Salt does leach out to the surface of Egyptian paste after firing. I have observed this on some of my earliest sculptures made with recipes used on the outset of my investigation into Egyptian paste. I suspect this weakens the sculpture over time. So I change to a recipe that doesn't do it as much. I'm experimenting with a number of things “fixes” to get rid of this dandruff like growth on my sculptures. Namely:
· soaking them in vinegar, or just plain water
· just washing the stuff off when it forms
· refire
· Another experiment, I've been meaning to try is adding borax to the Egyptian paste mix.
· Less sodium bicarbonate.
· Substitute washing soda for the baking soda.
· Fire hotter
. A sealer could be employed to stop the absorption atmospheric moisture and plug any pores in the fired Egyptian paste
· Perhaps the addition of a low fire frit
We just had to experiment to find what works. I've been searching for information on Egyptian paste; one of the reasons I started this blog is because there's not much information available on Egyptian paste.
You have some beautiful glossy beads on your website. It doesn't appear that you're having any trouble with "bloom"; what a luscious name for such an unsightly phenomenon. Perhaps this is only a problem with larger items. Should I find a solution I'll make a post of it.
------------- Anitra
Hi Anitra,
thanks for your reply. The photos of the beads on my site are of beads I made 5 years ago in Australia and I did not add salt to those bead recipes - so therefore there is no salt bloom on those.
However since I relocated to the UK (such a different climate) I have had months and months of problem solving to get my original recipes to work. It seemed no matter what I did and what amounts I adjusted the beads would not fire to a glossy finish like the ones in Australia - the Uk beads always came out slightly porous and rough and not attractive to make jewellery with as is the purpose of my beads. It was only after consulting a ceramicist here who suggested adding a little salt did I discover the effects of the salt and how it seemed to help the glaze melt together properly. I have discovered some interesting results with the addition of salt in terms of when it is added, how it is added and how much is added. I have had to lower my fire temp from 1040 C to 1030 and 1015, depending on the colour - otherwise the beads are just sticking to the wires.
So the first lot of beads I have fired with salt are about 3 months old and as of yet I have not noticed a bloom or scum from the addition of salt. If they were to develop a scum I wonder how long it may reasonably take? But judging by what you have said this could happen alot further down the track?
Of course because I am making and selling jewellery this could be a potential problem. If I felt there was any way around not using salt to still create a nice gloss then I would pursue it. But as I said I have tried all sorts by adjusting Soda bicarb, soda ash etc and none of those have really helped.
I use silica, soda feldpar, soda ash, soda bicarb, kaolin and a little bentonite in my recipe ( and now a little salt - the salt is diluted into the water I use to mix the paste - I literally add maybe half a teaspoon to about 100 mls of water). I think perhaps the reason I may not have ever needed to add salt in Australia was because there was so much humidity and salt in the air that it was enough to aid the crystal formation during drying and firing.
I also note that Susan Peterson uses salt in her recipes.
I have tried using borax in the past and found it gave the wrong results for me - it made the beads very unattractive and effected the colours dramatically.
cheers Kriket
Salt! You say? You may have save us months of running up blind alleys. Susan had wrote brushing with a little salt water would aid in crystal growth, but I had not thought of mixing it directly in the paste mixture. What a capital idea, Kriket!
Susan Peterson died just a year ago. She lived just two towns over from here. I now regret I didn't spend more time under her tutelage when the opportunity presented itself. The wealth of information that woman possessed will be missed. She left us with a fantastic book and a daughter, Jan Petersen, who will take up from where she left off.
I have tried brushing salt straight onto the beads just before firing and it works as well - literally let a small soft paint brush touch and soak the bead and then fire them slightly damp. I have tried brushing soda bicarb straight on and that did not help much.
I have pages and pages and pages of notes from all the experiments I have done in trying to solve mysteries of EP and on numerous occasions have come very close to giving up on my EP recipes but now I am glad I persevered and they seem to be 'working' again - for now.....
I would be happy to share thoughts if ever needed.
Kriket, I've just sent you an invite to join in on this blog as an author. Your knowledge and experience will help all of us form better Egyptian paste art. ------------Anitra
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