How (Not?) To Glaze A Crucible (experiment)

In which JF tries to improve his homemade crucibles with a simple borax glaze. Amazingly, it seems to work and the stage is set for the final test.

Twitter: @goodandbasic
Instagram: @good_and_basic

[ethankaminski]

Hey, tip from an amateur potter: try getting your glaze chemicals to be suspended or dissolved in water, and then apply it while liquid (by dipping, pouring, or painting). If it works the way I'm accustomed to, that'll let you apply the raw glaze while the pottery is cold, rather than faffing about with red-hot pottery that you can't touch.

I haven't used borax on its own, but the glazes that I have made, have normally been thick goopy suspensions of various mineral powders in water. Works quite well when applying it!

[dhawthorne]

The easiest glazeing process would be to throw salt into the kiln during the hottest part of your initial firing. Salt can burn around 300F but in the super high temperatures of a furnace it melts (around the same temperature for forging and hardening steel). It will then evaporate and the salt ions react with the silicon in the clay creating an orange colored glassy surface. There is no second firing needed.
Another good glaze is tin glaze. Mix a slurry or lead oxide and a little borax and paint it onto fired pottery. Once that dries, paint on a layer or two of tin oxide and borax. The borax is just a flux to help the glaze flow better and heat more evenly during firing. After this has dried for a day or two, get your furnace going full heat while preheating your pottery on an open fire then move them quickly to the furnace. This will produce a white glaze.

The key to both of these methods is to allow the pottery to cool as slowly as possible afterwards. Rapid cooling will crack the glaze. A good rule for pottery work is not to remove it after firing with anything but your bare hands. If it's too hot to touch, it's likely too hot to be exposed to ambient temperature air.

[butterflygroundhog]

I like how you post your learning experiences, whether they are failures or not. Identifying possible reasons of failures is as important as recording successes, and its great to see the progresses and the attempts. I wish more people knew about your channel.

[TheExalaber]

I would like to caution you that a cracked crucible is very likely to break when full of hot metal.

[ianlevine]

I wouldn’t worry about the puddles. I believe borax is also a common fluxing agent for separating impurities from your melt and bringing them to the surface to skim off.

[lithostheory]

Very interesting, loving this series!

[DheeBheee]

A couple comments touched on this, but Borax begins to melt before all of the chemically bonded H20 separates. Glazes with Borax will bubble up as that water finally separates and forms steam bubbles within their now-liquid surroundings, then the bubbles pop and the glaze settles down again (hopefully). This makes it tricky to use as a glaze on its own, though still possible, as you showed.

Borate does not contain chemically bonded water, so a glaze made from Borate (which is the vast majority of low-fire glazes) will behave better in the kiln. Gerstley Borate is the most commonly used source, though you have to order it from a pottery supplier so it isn't quite as good and basic as Borax.

[rodentnolastname]

Looking forward to the results. Was planning a similar attempt and the exact same thing.

[NSaw]

Cool! I'm working on firing a small plate I made from some clay I processed, it's the first time I've done anything with clay.

[TheRattyBiker]

I know this is 4 years too late, but I shouldn't imagine excess borax is a problem as its used as a flux in forge welding so it helps prevent oxidisation and makes for a cleaner bond, in this case it may just mean more slag floats to the top so could lean towards a lesser yeild but of a purer metal 🤷🏻🤷🏻 don't know. I'm not a scientist but that would also make sense.

[tommysmith]

The borax puddles shouldn't be a problem as borax is oftenly used as a flux to protect the molten metal from oxidation from the atmosphere

[adragontattoo]

Borax is used as flux so you shouldnt have too much of an issue there.

[AustralViking]

No personal experience, but I understand that with salt glazing, (which I suppose Borax is a form of) the salt is thrown into the kiln and it basically vapourizes and then deposits onto the pottery inside, Not sure how to do this in your situation but may be worth considering.

[MckayCloward]

Maybe apply the borax using a flour sifter. You could get a more even dusting this way.

[plusmanikantanr]

why don't you use Oven Mitts ? seems like any hot surface or item would automatically make you want to reach for oven mitts ...

[CaptnApathy]

I believe that green color is from the ashes from the fire. I remember reading that one of the earliest glazes used in china, which made that nice green was ash.

[dattebenforcer]

Nice, as a follow up from my last post, borax is also used to reduce the melting point of glass, and unlike wood ash it actually allows for making clear glass.

I thought you were only using ingredients from your backyard so I didn't mention it last time.

If you plan to use borax, maybe mix it with your clay next time you try making pottery. Cheers.

[cadeb]

just a guess but maybe a flour duster would help in applying a thin layer of powder

[rogerlibby]

Here is a wild idea. Thin out a water based flux with water, mix borax into it and paint it on the crucible then fire it.

[Kineth]

I don't have helpful feedback, but I do have a (maybe humorous) joke:
A police officer pulls over an automobile that was exhibiting erratic behavior.
Officer: Good evening sir, I see that your eyes are glazed, have you been drinking tonight?
Driver: Hello Officer, I see that your eyes are glazed, have you been eating doughnuts?
-fin-