The quest of an ultra-clear glaze on terra cotta

Share from Insight-live.com (Lab Documentation and Calculation System) by Digitalfire. https://digitalfire.com

It is likley to be a combination of glaze chemistry, thorough melting, slurry preparation, application thickness, firing, choice of clay body.


Cone 04 UltraClear Low-Expansion

Code #

G3879C

Materials Amt
Fusion Frit F-524 750.000 73.17%
Fusion Frit F-69 140.000 13.66%
New Zealand or Grolleg kaolin (Grolleg Kaolin) 90.000 8.78%
Silica 45 micron (Silica) 45.000 4.39%

Total:1,025.00

Auto Unity Formula

BaO 0.04
CaO 0.38
MgO 0.18
K2O 0.09
Na2O 0.10
(KNaO) 0.19
SrO 0.22
B2O3 0.74
Al2O3 0.47
SiO2 3.76

Ratios

Si:Al: 8.0:1
SiB:Al: 9.6:1
R2O:RO: 0.2:0.8

Expansion

6.2 (Molar:5.8)

LOI

1.1

Cost

0.00 per kg

Notes

*An adjusted version of G3879 to reduce thermal expansion. It switches the silica to 45 micron (325 mesh) for better dissolution in the melt. And it increases the frit low-expansion F-69 (the Fusion equivalent of Ferro 3249) at the expense of F-524.

This also switches to whiter burning kaolin (New Zealand), that improves transparency and removes the amber coloration.

It still fires to the same crystal clear on light burning bodies (but clouding on terra cottas unless applied thinly). And is fitting pieces better.

For a dipping glaze we mix 1500g powder to 1125g water (57%/43%) to get a specific gravity of 1.54. This produces 1.7 litres. This builds up thickness quickly on Snow clay (because it is so absorbent).

For a brushing version we mix 350g powder with 5g Veegum and 5g CMC gum, shake this an add it to 450 water and then mix in a kitchen blender. This produces a gelled slurry that paints well.

Pictures

G3879C is firing much whiter, why?

Cone 04. All three clear glazes are on the same body. Left to right: Amaco LG10, G3879C recipe, Crysanthos SG213. The middle one employs Fusion Frit F-524, it is more expensive. But look at the benefit: It fires much more transparent so the piece is much whiter. And it is not crazing or pin holing. And it is glossier.

G3879C, G1916Q, G1916QL1 on L213 Cone 04

The move from ball clay to New Zealand kaolin (centre mug vs right mug) greatly improves the clarity (because of the reduction in iron and titanium).

G3879C vs. G1916QL on L4410K low fire white

The iron from the ball clay is the reason the glaze on the right is off-white.

Cone 04 G1916QL1 vs G3879C melt flow comparison

G1916QL1 is more melt fluid so it is likely useful before cone 04. But G3879C is also very fluid (it also has a higher surface tension). Both are producing textbook high quality flows.

G3879C, G1916QL1 on L4410L Bisque 1800 glaze cone 04

No crazing after weeks of use, ultragloss.
Frit 524 has much less iron, that is why that mug is so much whiter.
After several months at home the G3879C did craze.

G1916QL1. G3879C, G3879G1 on L213 tiles - Cone 04

These are all craze-free after several months.

G3879C on L4410P dolomite body at cone 04

The outside glaze is Spectrum 336. The G3879C is our recipe, a base transparent that we have been tuning to reduce the thermal expansion as much as possible to fit our 50:40:10 BallClay:Dolomite:Nepheline body. The result is glaze compression, it is now under enough compression on the inside of this piece that it is forcing it apart.

G3879C on L215, Buffstone at cone 02

G3879C on L4170B at cone 04 with L3685Z6 engobe

No crazing after six months or more.

Testdata

LDW - LOI/Density/Water Content

WWGT DWGT H2O LOI DENS
111.46.4343.6%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04 UltraClear Low-Expansion" id="202474" key="WWmZKmwo" date="2022-12-19" codenum="G3879C"> <recipelines> <recipeline material="Fusion Frit F-524" amount="750.000" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="140.000" tolerance=""/> <recipeline material="New Zealand or Grolleg kaolin" lookup="Grolleg Kaolin" amount="90.000" tolerance=""/> <recipeline material="Silica 45 micron" lookup="Silica" amount="45.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2019-04-15, Modified: 2022-12-19 22:22:22

Cone 04+ UltraClear Glossy Base

Code #

G3879E

Materials Amt
Fusion Frit F-524 85.000 84.16%
Ferro Frit 3110 5.000 4.95%
Silica 10.000 9.90%
VeeGum 1.000 0.99%

Total:101.00

Auto Unity Formula

BaO 0.04
CaO 0.45
K2O 0.10
Na2O 0.16
(KNaO) 0.26
SrO 0.24
B2O3 0.58
Al2O3 0.32
SiO2 4.03

Ratios

Si:Al: 12.7:1
SiB:Al: 14.5:1
R2O:RO: 0.3:0.7

Expansion

6.8 (Molar:6.4)

Cost

0.00 per kg

Notes

*This adds more SiO2, less Al2O3 and less B2O3 seeking fewer microbubbles than G3879C.

A brushing version made by blender mixing 340g powder, 440g water, 6g CMC, 6g Veegum.

Clouding was worst with this.

Pictures

Three clear glazes on L215 at cone 04

G3879D - Good transparency but shivering enough that it is hazardous to pick up the mug for fear of glass slivers
G1916Q4 - Shivering on white engobe but not as bad as D.
G3879E - No shivering but clouding the worst.

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04+ UltraClear Glossy Base" id="228221" key="4hWAR8vC" date="2022-12-19" codenum="G3879E"> <recipelines> <recipeline material="Fusion Frit F-524" amount="85.000" tolerance=""/> <recipeline material="Ferro Frit 3110" amount="5.000" tolerance=""/> <recipeline material="Silica" amount="10.000" tolerance=""/> <recipeline material="VeeGum" amount="1.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2019-04-15, Modified: 2022-12-19 22:20:16

Cone 04+ UltraClear Glossy Base

Code #

G3879F1

Materials Amt
Fusion Frit F-524 65.000
Old Hickory #5 Ball Clay 15.000
Fusion Frit F-75 10.000
Fusion Frit F-69 10.000

Total:100.00

Auto Unity Formula

BaO 0.03
CaO 0.38
MgO 0.13
K2O 0.08
Na2O 0.19
(KNaO) 0.27
SrO 0.19
B2O3 0.63
Al2O3 0.47
SiO2 3.76

Ratios

Si:Al: 8.1:1
SiB:Al: 9.4:1
R2O:RO: 0.3:0.7

Expansion

6.7 (Molar:6.3)

LOI

1.4

Cost

0.50 per kg

Notes

*This variation seek better melting to be ultragloss. Both 3110 and 3249 should help with melting the frit 524 better.

To make a brushing glaze test we mixed 340g powder, 400 water, 5 CMC, 3.3 Veegum. This produced a good gel out of blender (so it may be too gelled tomorrow). SG 1.36.

Good results so far, this has produced the best transparent on terra cotta so far. That being said, it is still not ultra gloss, will try firing to cone 03 also.

Pictures

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04+ UltraClear Glossy Base" id="228330" key="d1eak2nY" date="2022-12-19" codenum="G3879F1"> <recipelines> <recipeline material="Fusion Frit F-524" amount="65.000" tolerance=""/> <recipeline material="Old Hickory #5 Ball Clay" amount="15.000" tolerance=""/> <recipeline material="Fusion Frit F-75" amount="10.000" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="10.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2019-04-15, Modified: 2022-12-19 22:25:45