Everyone is adding B₂O₃ into glazes: boric acid, borax, colemanite and ulexite. How do you choose?
Recently, many customers have enquired about boron-containing frits, and I keep running into one familiar question.
A customer asked me: "I just need to introduce some B₂O₃ into my glaze. Aren't boric acid, borax, colemanite and ulexite all the same?"
At first glance, this statement sounds reasonable.
All of them supply boron oxide. But once you substitute them in a glaze formula, the result is often far from identical.
Although these materials all contain B₂O₃, they bring along totally different accompanying oxides.
Boric acid mainly delivers boron; borax introduces B₂O₃ together with Na₂O; colemanite carries B₂O₃ and CaO; ulexite supplies Na₂O, CaO and B₂O₃ at the same time.
So the real question is not:
"Which one has higher B₂O₃ content?"
Instead, it should be:
"What oxide does my current glaze formula actually lack?"
Let's start with boric acid: straightforward, yet not always trouble-free
If your only goal is adjusting B₂O₃ without altering other oxides significantly, boric acid is the most direct option.
Its oxide calculation is simple. However, glaze technicians working with wet glaze slips know its unavoidable downside - solubility in water.
Once dissolved in the glaze water, boron may migrate during glazing, water absorption and drying, instead of staying evenly distributed.
Your formula may look perfect on paper, yet face inconsistent local boron concentration on mass production lines.
That explains why some formulas work well in lab tests but become unstable in continuous manufacturing.
Boric acid itself is not bad. Its suitability depends on whether your production process can handle its properties.
Next, borax: boron comes in, along with sodium
Borax does more than provide B₂O₃; it also adds Na₂O, a powerful flux.
For low-temperature glaze systems, borax can effectively lower melting point and improve melt flow.
On the flip side, if your base glaze already has high alkali content from potassium and sodium, adding borax for extra boron will further raise Na₂O levels.
This changes melt fluidity, thermal expansion and chemical resistance of the finished glaze.
It is also water-soluble. So I would never simply claim "borax works better than boric acid".
They serve different purposes.
Colemanite works in another way
Colemanite is a natural calcium borate mineral. Its name tells its core composition: boron + calcium.
It is a handy boron source when your formula requires extra CaO.
But if your formula already contains plenty of calcite, wollastonite or high-calcium frits, replacing boric acid directly with colemanite changes not only boron content, but also CaO.
That is a common scenario: customers adjust formulas to keep identical B₂O₃, yet get completely different firing results.
The root cause is simple: equal B₂O₃ does not mean an identical glaze system.
As a natural mineral, colemanite is also affected by ore origin, associated impurities, loss on ignition and particle size.
Industrial chemicals and natural minerals behave very differently.
Ulexite: three oxides delivered in one package
Ulexite is even more unique. It brings Na₂O, CaO and B₂O₃ together.
For this reason, I avoid calling it a "natural alternative to boric acid" or a simple borax substitute.
It acts as a pre-combined boron‑sodium‑calcium system. It performs excellently when your glaze needs all three oxides.
If you only intend to tune boron without shifting sodium and calcium levels, it may create extra complications.
Natural ulexite also contains structural water, which releases during heating.
This must be considered for fast firing, thick glaze layers or narrow firing windows.
That is why some technicians achieve stable results with ulexite, while others encounter pinholes and mottling after switching.
No experience is wrong here. You are just running different formulas and firing cycles.
The substitution mistake I see most often: direct weight-for-weight replacement
For example, replacing 5 parts boric acid with 5 parts ulexite.
This shortcut seems easy, yet it disturbs the whole glaze system.
Different boron sources have varying B₂O₃ concentrations. Even after you equalise B₂O₃ dosage, you still need to calculate the extra Na₂O and CaO introduced.
Once sodium and calcium shift, proportions of feldspar, calcite, wollastonite and frits may all need rework.
Proper substitution is never "swap 5 parts for 5 parts".
Calculate B₂O₃ first, then account for the accompanying sodium and calcium. That is correct formula adjustment.
Here is my practical selection logic
I am not ranking these raw materials.
I only pick based on what my glaze system needs.
None of these materials is inherently superior.
A raw material works well only when it matches your formula requirements.
This also explains the widespread use of boron-containing frits in our industry.
Boric acid, borax and other boron sources are functional, yet they carry inherent drawbacks: water solubility, ion migration, slip instability and uncontrolled co-introduction of alkali/alkaline earth oxides.
Manufacturers pre-fuse boron with other raw materials into stable glassy boron frits to solve these issues.
This is not overcomplicating the process.
On the contrary, it locks the mobile boron inside a stable glass network.
The resulting glaze slip is easier to control, with far better batch-to-batch consistency.
This is why we have been developing our new series of boron-containing frits.
We are not launching extra grades for the sake of expansion.
Customers have diverse requirements: firing temperature, transparency, melt flow, thermal expansion and target boron content all vary.
Some need lower firing temperature;
Some prioritise high clarity;
Some want high boron without excessive potassium and sodium;
Others focus on slip stability and repeatable batches.
These demands cannot be covered by a generic "high-boron frit".
I would love to hear from you.
Are you developing boron-based glazes, or hesitating over replacing boric acid, cutting borax dosage, switching to colemanite or ulexite?
Feel free to share your firing temperature, glaze type and current boron source in the comments.
I am curious which boron material you rely on in daily production.
We are currently conducting firing tests on our new boron frit range.
If you are sourcing this type of product and wish to run side-by-side trial firings, leave a message to get in touch.
