What makes a frit "soft"?

[Martin Webb]

 

 

Can anyone explain what makes a frit soft, and if it's aligned with it being High Expansion? Is it the alkaline content (potassium and sodium) or does the calcium contribute too,  also what percentage of Alkaline or Calcium does it become soft?  I understand that Borax increases the expansion but does a high Alkaline content counter this?  Frit 3134 has Alkaline and High Boron!

 

I have a local reduction glaze recipe which uses a soft borosilicate frit, I tried frit 3110 which didn't work. I have conflicting info about whether 3110 is soft or not.

 

 

[Hulk]

Hi Martin!

No doubt you'll get more responses from other forum members. In meantime, from Tony Hansen's site:

 F3134

Oxide	Analysis	Formula
CaO	19.51%	0.68
B2O3	22.79%	0.64
SiO2	45.56%	1.48
Na2O	10.14%	0.32
Al2O3	2.00%	0.04
Oxide Weight		195.57
Formula Weight		195.57

 

 F3110

Oxide	Analysis	Formula
CaO	6.29%	0.29
K2O	2.36%	0.07
Na2O	15.24%	0.64
B2O3	2.64%	0.10
Al2O3	3.70%	0.09
SiO2	69.77%	3.03
Oxide Weight		261.11
Formula Weight		261.11

Looks like 3110 doesn't have much boron.

Can you define "soft" as you are using? Please also copy the glaze formula, firing targets, clay type(s), and what happened with the frit substitution you tried.

[Martin Webb]

The recipe asked for a "Sort Borosilicate frit" the frit I tried (3110) blistered instead of giving a local reduction. I need to know how to assess how soft each frit is so I can work out what others to try. 

Recipe:

SBF, 90%

China Clay, 6%

Silica, 4%

Tin, 2%

Copper Carb, 1%

Plus Silicon Carbide up to 3% 

Temp is 1080 and using a white earthenware. 

[Bill Kielb]

Hi Martin, 

Similar questions as @Hulk as soft has litttle meaning to me.  I find the recipe specification to be a bit vague but here is an idea to contemplate.

• The reducible items in your recipe will basically be copper along with the tin
• The silicon carbide is what you are counting on for reduction

The frit needs to melt at  about cone 04 which likely means the recipe in a glaze calculator should likely have about .45 boron which is a common way to make things melt by cone 04. So without knowing the meaning of soft it would seem the 3134 is more useful than the 3110 just by examination of the boron content of each.

3110 being a low boron source and 3134 being a relatively high source of boron. Not sure that helps but just my first impression and a reason to try the 3134.

I assume the intended look is some form of copper red, just an assumption though.

[Min]

@Martin Webb, which  frit  did the recipe call for? 

Chart below from Potterycrafts, you can see that their P2963 Soft Alkaline frit has 0 sodium and a tiny amount of potassium. If we know the analysis for the frit you are trying to substitute for someone could probably do a conversion for you. Boron is a low expansion oxide whereas sodium and potassium are high expansion oxides. 

Welcome to the forum.

Which frits do you have?

 

[liambesaw]

I think soft in this instance is low viscosity, will help the bubbles from the SiC heal over

[Martin Webb]

Hi, thanks for the replies Hulk, Bill Kielb and MIn, I'm glad I found this forum!

There was no analysis with the recipe, the whole issue is I don't know how to define  "soft"  the glaze is from Greg Daly's Developing Glazes and gives a dark burnt effect with just a touch of red. 

[Magnolia Mud Research]

In the parts of glass world, especially the art glass subset, the "soft" and "hard" meanings are explained by: 

“Hard-glass” is an acronym for borosilicate glass, like Pyrex or Kimax. “Soft-glass” is an acronym for soda-lime glass, or a higher expansion type glass, (88-92 COE). Lab glass is generally made from “hard-glass”, (borosilicate). Bottles are generally made from “soft-glass,” or soda-lime glass.
https://www.aceglass.com/dpro/kb_article.php?ref=3469-WAHX-5341

since frits are nothing but powdered glass, it does make sense that soft and hard frits would fall in to the same meanings.  

The origns are jargons from "way-back-then".

LT

[Min]

Anybody have any more soft frit analysis info? I noticed Potclays has a "Soft Borax Frit" but I don't have the analysis for it. When I look up Potclays 2264 noting comes up.

[Magnolia Mud Research]

more on soft/hard:   from Hamer 6ed. page 352:

"SOFT
Low temperature. In describing glazes the term means 600 °C to 1050°C(1112°F to 1922°F).  Soft fluxes are those which can be used for these glazes and include oxides of sodium, potassium, lead and boron.  Soft glazes are physically soft and are easily scratched. 
Soft as relative means at a lower temperature not necessarily referring to below 1050°C.  See also Hard(2)". 

pg. 174
"Hard(2).
Hard, medium and soft are relative terms describing firing temperatures.  Hard means high temperature, e.g. hard earthenware, hard-paste porcelain.  The term harder is relative and when used against an example could mean merely 10° or 20° higher in temperature. 

In describing glazes, soft means 600°C(1112°F to 1922°F), medium 1050°C to 1200°C and hard 1200°C to 1400°C.  Hard glazes therefore melt at temperatures above 1200°C. They are also physically hard and are not easily abraded.  Soft glazes are physically soft and scratch easily. 

Hard fluxes are those which work at the higher temperatures but not at the lower ones.  Magnesium oxide, for example, does not start its action as a flux until 1170°C and therefore is useful in glazes only above this temperature.  Wood ashes are often classified as hard, medium or soft according to the temperatures at which the will act as fluxes.  Ashes which contain more silica than flux are classed as hard.  Paradoxically, hard ashes often come from soft woods. 
Cornish stone is also classified as hard or soft but this refers to its physical property.  The hard Cornish stone is the softer flux." 

Ain't jargon wonderful?

LT

[Min]

Okay so if we go by Hamer's "Soft" definition that would exclude the Potterycrafts Soft Alkaline frit as that contains over 25% calcium oxide.  We know 3110 is a high alkaline frit with  very high K2NaO so is it referring to frits high in the alkaline earth metals as being soft frits?

 

[StonedStudio]

You could reason another possible definition of "soft" would be "low amount". 

The P2963 "Soft Alkaline" has only K2O as an alkaline oxide. In the amount of 0.3%. 

 

 

My guess would be that something else is the issue in your glaze that didn't work, and not the 3110 you used in the glaze.

[neilestrick]

4 hours ago, Martin Webb said:

The recipe asked for a "Sort Borosilicate frit" the frit I tried (3110) blistered instead of giving a local reduction.

It's really easy to get bubbling when using silicon carbide for localized reduction. I would test the glaze melt without the carbide first, to see if the glaze is acceptable in the first place. Chances are all the blistering was related to the silicon carbide. 3124 would work well in that recipe, as it's just a basic low fire clear glaze. You'll need to test the silicon carbide at different percentages, but I would say start very small, like 1/4 of 1% and move up from there. It's very easy to get too much. You'll also need to experiment with the mesh size of the silicon carbide. Too large a grit doesn't work. I would start with about 600 mesh, and if that doesn't work test finer grades, like 800 or 1000 mesh. I'd also play with firing schedules to see if adding a hold somewhere around cone 014-08  will help get good burnout of the silicon carbide before finishing the firing.

[Min]

I like Neil's idea of using 3124 instead, @Martin Webb, if you don't have 3124 which frits do you have available to you? 

Still would like to get a definition of a soft frit.

[Babs]

"Blistered instead of local reduction"

Could it be because of quantity of silicon carbide?

Try 4108 or 4124 if you have them so you may ve able to discount that frit is the prob

[Tamas]

Here's another frit called Soft Borax frit, classified in the MSDS as borosilicate frit: https://www.bathpotters.co.uk/soft-borax-frit

According to the website it's slightly alkaline.

[Martin Webb]

2264 is the frit I have no data for. 

19 hours ago, Min said:

Anybody have any more soft frit analysis info? I noticed Potclays has a "Soft Borax Frit" but I don't have the analysis for it. When I look up Potclays 2264 noting comes up.

 

 

[Martin Webb]

15 hours ago, Min said:

I like Neil's idea of using 3124 instead, @Martin Webb, if you don't have 3124 which frits do you have available to you? 

Still would like to get a definition of a soft frit.

Yes I have 3124, so will try it, also have 2963 and 2264, just no data for 2264. 

[Min]

I contacted the tech dept at Potclays and asked for the analysis for 2264, the reply I got was that they themselves have repeatedly asked the manufacturer for that info but it hasn't been forthcoming. They will pass the info along to me if/when they receive it. In the meantime they did share a link to Potclays frit analysis, looks the same as what I posted above but in a different format. Link to that here.

When I asked what constituted a "soft frit" the answer I was given is "‘Soft’ in the context of 2264 refers to the higher flux content of the frit" . 

Thanks for letting us know which frits you have Martin. I went ahead and plunked in the 3 different frits you have into the base recipe (I left out the colourants and silicon carbide). If you are going for a well melted durable glaze the 3110 is out as is the 2963. 3124 version looks good.

[PeterH]

22 hours ago, Min said:

Anybody have any more soft frit analysis info? I noticed Potclays has a "Soft Borax Frit" but I don't have the analysis for it. When I look up Potclays 2264 noting comes up.

Searching for 2264 potclays I get a rather cryptic link to FRIT FORMULAE - Potclays  Which can be used to view or download a 2-page list of frits and their composition.

Unfortunately for 2264 the entry is Composition not disclosed, which sounds like an intentional decision.

[Min]

1 hour ago, PeterH said:

Composition not disclosed, which sounds like an intentional decision

Yup! That's what it says on the link I posted 2 up from this one. Plus the answer I recieved from Potclays in regards to what a soft frit definition is isn't very clear. Using my logic if a frit is high in fluxes then proportionaly it will be low in silica and/or alumina and that's not the case for Soft Alkaline P2963 which has obviously has the term "soft" in it's name so one would assume that's a "soft" frit.

[Martin Webb]

Thanks for that link PeterH, and everyone I've had a great introduction to your forum. I have some 2264 so will try it out, as well as 2963 and 3134. 

[Babs]

7 hours ago, Martin Webb said:

Yes I have 3124, so will try it, also have 2963 and 2264, just no data for 2264. 

3124 sold in Auz as 4124 these days and named 4124 as equivalent. Thought as using Daly's book you may be in Aus.

You might have yourself a nice crater glaze!!

[Min]

Potclays finally heard back from Potterycrafts regarding their frit 2264. They supplied very limited data but it is interesting as it does show the frit is comprised of only silica, calcium and boron. (don't know why it says G-239 as a reference number)

[Babs]

I noticed that the frit list I have , and may be totally irrelevant AND coincidental , that the hard frits are also described as clear. Soft frits do not have clear as part of their description.