Functional..foodsafe.

[Babs]

I was reading an article in a Ceramics Monthly last night. The article had a tag of functional glazes. One of the recipes, which was being used on a dish for serving food had 95 Barium Carbonate.

How do people feel about this. I realise the term functional is broader than food safe.

[C.Banks]

95% BaCO3 sounds more like a stain and certainly not anything I'd want to use as a glaze. iirc barium *not correctly remembered* can float around and flash on pieces even after the original firing?

 

food safe = functional for me

[Babs]

Sorry, caps not used.9% Barium Carb.

[Min]

When fired, barium, whether from barium carb, sulfate or fritted form has to be locked up thoroughly in the glaze to be non-leachable. Functional pots need to be tested for leaching, only way to know for sure. Even then underfiring a load could easily produce a glaze that might be stable at maturity temps but leaches when underfired. As with anything the dose makes the poison.

 

No barium of any form in my glazes. It’s just not worth the risk, to me making up the glaze nor for the final user.

 

I agree with C.Banks, functional means food safe and durable.

[Guest JBaymore]

First of all it is about the FORM of the chemistry as to the potential toxicity and the particular routes of exposure.  If you just think about "Barium" sort of generically as a single thing, you likely need to narrow things down a bit.

 

An example:  Barium CARBONATE is a relatively toxic substance upon ingestion (soluble in stomach acid....not so much in water).  However, Barium SULPHATE is not and is used in gastrointestinal x-ray procedures.  The Ba⁺²  ion and the very soluble in water chloride, nitrate, and hydroxide forms are well known to be toxic. 

 

Once again.. the main hazard from barium carbonate is to the potter handling the raw material (mainly inhalation and ingestion).  See MSDS for what you use for ALL materials.

 

Chronic exposure to low levels of Barium OXIDE....... that which is what is left in the glassy matrix after barium carbonate is fired (but see below)...... well.... not much info or studies on that very specific issue, which is what we are concerned with when we talk about that nebulous term, "food safe".  How well tied into the matrix the barium ions are...... only testing will tell for a specific formulation, application method, and firing profile.

 

Barium oxide is known to be toxic... but typically in acute situations.  Chronic long term studies... typical of leaching into food stuff....... have not found too much info.  Studies say that only about 5-30% of the total barium compounds that are ingested are actually absorbed into the body.  So leaching would likely have to be substantial to be of a huge concern. The chronic long term MRL (Minimum Risk Level) is set by most studies as 0.2 mg/kg/day.  For a human of about 175 pounds / 79 kilos that would be ingesting 158 mg per day for at least a year. 

 

Note that barium carbonate sometimes has some issues in dissociating into barium oxide (what acts as a flux) in firings.  When that happens you have little "flecks" of barium carbonate particles suspended in the glaze melt.  In THAT case......... you are dealing with a much higher likelihood of leaching of a clearly toxic substance into foodstuffs.

 

Formal lab leaching tests would be in order.  As a minor secondary flux, it is likely in my opinion that such a level of BaO in a glaze is not an issue.  Too little of it there to be enough to cause issues.  Stuff like those beautiful, gorgeous, barium blue matts?  That is where some real issues very likely would lie.

 

Prudence issues again here like in the manganese discussion elsewhere.  Glass half full or half empty?  If you don't KNOW that a hazard actually exists, does that make it safe?

 

best,

 

......................john

[Tim T]

The other consideration is where the barium glaze is applied. If inside the vessel, or close to the rim on a drinking vessel, then one needs to be careful about the glazes. But if on the outside (like, coincidentally, in the barium blue streak in my pot picture), then I think the risks of a customer licking the surface of the pot sufficiently to have an toxic effect are acceptably low for all but the most paranoid.

[Pres]

We have had this discussion before. As I have said earlier, when I became aware of the hazards of barium to me and my students, I had it removed from the classroom to be properly disposed of. I only had around 3lb. of it. I do not use it at home, and have never had it here. I try to be careful about how my materials are stored, how I handle them, and how I clean up after using them. . . but accidents do happen. Most of my chemicals in except for coloring oxides are pretty safe other than silica content. . . another story.

 

 

best,

pres

[Mark C.]

This is personal decision on how to or if one should use a given material

I use a little barium glaze on the outside of a few forms,it is not on the inside or the lip of the form just the outside so it would be hard to have it leach onto a customer. I use all the precautions handling it in its various forms.

If I was a hobbyist I would avoid it's use

I also have used strontium as a substitute with less colorful results

This is one of those materials that require special thinking about and is not for everyone

Many years ago Otto Hieno summed up this use of this material for me

You need to pay attention using it.

I do.

[neilestrick]

I think it's safe to assume that the term 'functional', when used among potters, means food safe. I don't know what else it would mean. But unless the author of that article has had that glaze tested, it shouldn't have been tagged as such.

[Chilly]

Functional = having a function.  So a ceramic lamp base could be functional.  Looking around my home I have a number of items that are ceramic and functional that I wouldn't dream of eating or drinking from.  Possible, but just not practical to do so.  So, for me, functional does not equal food safe.