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Struggling To Get A High Gloss Cone 10 Transparent Base. What I've Tried So Far...


MartinB

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Hi there,

 

I've recently started making my own glazes and one thing I'm struggling with is achieving a super smooth transparent to use by itself but also with stains and oxides.

 

My benchmark is Scava's Porcelain Transparent (http://www.scarva.com/en/Scarva-GZ2305-Porcelain-Transparent/m-249.aspx) which has a very high gloss surface finish with hardly any imperfections. The cost of this though quickly add's up having several buckets on the go with it as the base.

 

I've been reading John Britt's 'The Complete Guide to High-Fire Glazes' and tested most of the transparent recipes listed (Leach, Hamada, Standard, Limestone, Shaner) which are all a combination of Custer Feldspar, Silica, Whiting and Kaolin in various ratio's but none have as smooth a finish as the commercial glaze.

 

They're not pinholing/crazing/bubbling, but there's a very fine surface texture which I'm not happy with. They've all been fired in the same kiln which is known to cool quickly, 30min soak and cones are showing its hitting cone 9.

 

I'm going to do another round of testing this weekend but was looking for any tips on things I could try.

 

  • The test tiles all came from the same bisque firing so I don't think its organic's burning out when its high fired.
  • I'm going to try sieving the mix through a higher mesh, my last round of testing was through a 100
  • I'm going to substitute the whiting for Wollastonite (1.16 Wollastonite for each 1 of Whiting and 0.6 of Silica) as I'd read the Whiting releases lots of gas during firing and could cause micro bubble

I'm mixing the base glazes tomorrow to let them slake until I can apply them at the weekend.

 

The photo attached is with the commercial glaze and the level of gloss I'd like, the red/yellow/orange pinholed with large amounts of stain but were smooth with lower percentages.

 

Thanks for any help, its much appreciated.

Martin

 

Edit: I'll post some of my transparent tests tonight, the photos I had didn't really show the problem.

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I'll be interested to see the replies to your post Martin as I too like to work with a transparent base plus stains. On the successful test tiles in your picture, what % steins have you used? They look great!

 

The very successful transparent glossy glaze I tested (stoneware) had lead bisilicate in it which I was told wasn't really a good idea for anything functional. I haven't yet got back to trying an alternative.

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Attached is a side by side of the bought transparent and the best of the ones I made, these were all using Valentines Audrey Blackman as the body. Not sure why the image is sideways but the top tile is the homemade.

---------------

 

Thanks Celia. I'm really happy with how they came out (apart from the yellow and red) I've attached another image showing the rest.

 

Blue is just straight Cobalt, 0.5/1/2% all smooth

Purple is a mason stain, 1/4/8%, all smooth (the 1% is a really delicate pinky mauve)

Green is 1/3/6%, all smooth

Faux Celadon is bought premixed from Scarva and super smooth (I assume they use the same porcelain transparent base and then stains)

 

Yellow is 1%, 4% and 7%, the 4 was a bit pock marked and 7 a mess

Same with Reds

 

The Red and Yellow stains were bought from Bath Potters, I've tried them in their own brand base transparent, some homemade transparent and Scarva's transparent and anything over 2-3% makes a mess. I've got some of Scarva's stains on order to see if they work any better.

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I am 90% sure this one works well with audrey blackman at cone9-10. Smooth surface. Never used the clay myself but seen plenty of AB with this glaze on that looked great.

 

You could try adding some frit to an almost there transparent and see if that helps. I have tried taking out whiting and swapping for wollastonite with no change in glaze surface or bubbles. This glaze does use wollastonite though.

Transparent CollegeCode #G-5M	Materials	          Amt	Cornish Stone	         62.00	Wollastonite	         16.00	Kaolin	                  8.00	Talc	                  4.00	Petalite	          4.00	BPS Standard Borax Frit	  6.00Total:100.00 (g)
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Thanks Joel. I didn't get a chance to mix them up today so will do it tomorrow and give your Transparent College a go too, will have to check if the studio has any Petalite though, first time I'm seen it in a recipe!

 

Will report back when the next lot of tiles come out the kiln.

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So I just unloaded the weekends test tiles and things are looking very promising. I tested 3 different base glazes

 

'Standard' - which was the best of my last lot, new batch made as a control.

Digital Fires Transparent Base - Which is pretty much the Standard but with Wollastonite instead of Whiting

College Transparent - From above post by Joel (but with Spodumene instead of the Petalite)

 

All sieved to 120, left to sit for a day then sieved again before applying. Standard had the same surface texture as before, slight hint of orange peal effect. Digital Fires was much smoother, almost as good as the bought transparent, but had a slightly bluish tint to it. College Transparent was probably as smooth as the commercial and crystal clear, by far the best of the lot, across 3 different bodies too (porcelain, white stoneware and buff stoneware)

 

I also tested each base with the new Scarva Yellow and Red stains I bought, to 6%. Standard took both stains very well but still had the surface texture. Digital Fire Transparent took the stains well and was smoother than the Standard. College Transparent really didn't enjoy the stains, red wasn't too bad but yellow pin holed pretty badly.

 

So it looks like I'll go with College Transparent or Digital Fires depending on the situation. The next round of testing will be a wider range or stains and oxides and see how they both react.

 

Thanks again Joel, really appreciated!

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You're welcome, it is from Newcastle College ceramic department. Not sure who came up with it. Do you have some pictures of the tests? 6% seems like quite a bit and will be changing the glaze chemistry as you can see. Could be if you are colouring the glaze with that much stain each one could need a slightly different recipe to have the right surface.

 

Have you tried using it to colour slip or paint on as underglaze and using a transparent over that? It could help the problem but maybe lose what you are looking for in colour.

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I tried taking some photos but don't think it shows the surfaces that well.

 

From left to right, Standard, Digital Fires, College Trans, and the commercial trans on the top row.

 

Having spent a bit more time with them I think its a very close call between the Digital Fire and College. The top of the college one has a few marks where the glaze went on too thick (4 secs top, 2 sec bottom) but looks good on the lower half.

 

The 6% was just seeing how far I could push the stain/glaze. The last yellow stain I ordered bubbled terribly over 3%, I reckon the colour I'm after would be around 4% so should be good. I've never tried underglazing or using slips, its on my ever growing list of things to try out :) 

 

Also included a photo of this years test tiles, they were all in a big bag but was good to get them out and see what I've learnt!

 

Thanks again for your help.

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