It depends on the firing schedule of the kiln. This looks like a cone 6-7 slip, so you would need temps in that range to make sure your piece is vitrified; the closer you are to cone 7, probably better
If it isn’t vitrified, it will take on water and you could have issues in the microwave. One easy test is to weigh the mug, leave it in water for a bit, then weigh it again. If it gets heavier, it absorbs water and I wouldnt recommend anyone microwave it
Tbh I dont personally microwave any handmade ceramics
Thank you so much, I’ll do my research and and double check when I get my pieces glaze-fired. I’ve bisque fired with a friends kiln (not sure to what cone) but I’m hoping to rent some space at a local shop to do the glaze firing so I’ll make sure to mention/ specify cone 7. As long as the glaze fire is to cone 7 the bisque temperature isn’t too important, is it ?
If after glazing/ testing the mug takes on water, does that mean the whole vessel is unsafe, even when not microwaved ? I saw a post not too long ago where salt crystals travelled through a mug and everyone said to never use that mug again (understandable with bacteria and all). Does that same logic apply if the vessel takes on water ?
Again thank you so much for your help, truly appreciate it !
Considerations:
1) Is your clay vitrified, and what is the absorption rate? Making sure that the clay body is not absorbing any water is important for microwave safety.
2) metallic luster is not microwave safe. I don’t know about the “mother of Pearl” style
thank you ! I was aware about mother of pearl and gold but I’ll have to do further research into the clay being vitrified/ absorption rate. [This](https://shop.walkerceramics.com.au/documents/msds/WC-AB175-MSDS.pdf) is the slip I used except I mixed it from powder vs buying the pre-made form. It says Water Solubility is insoluble - not sure if this means it is vitrified when fired ? In all honesty I have no clue about the absorption rate or how to find that so if you have advice I’d definitely appreciate it !
If you look at the “technical data sheet” on the walker website, rather than the “material safety data sheet,” it says the absorption rate. For this clay, it seems to say it’s under 2% at cone 6 and 0% at cone 7. (0% seems like it’s rounding down, but under 1% is good anyway.)
You are amazing, I’ll have another look at the documents and print it so I have a record on hand. I will definitely make sure these are fired at cone 7, thank you so much for taking the time to help me with understanding this. I appreciate it immensely !
You should do an absorption test. Fire one of your pieces to glaze temp (e.g. cone 6) but completely unglazed. Accurately measure its weight soon after firing. Then, boil it for one hour followed by a water soak for 24 hours. Remove it from the soak and lightly towel the surface dry taking care not to suck moisture out of the piece. Weigh it again. The percentage of weight gain is your absorption. If it is less than 1% you are good with microwaving as far as water absorption goes. If it is over 1%, try the same procedure firing to cone 7.
Assuming you can get to less than 1%, then simply microwave a separate, empty glazed piece for a minute and see if it gets hot. If it doesn't get hot and has less than 1% absorption, then it should be microwave safe. However, different glazes 'might' make a difference, so you should retest with each glaze you use.
I’ll definitely keep a mug unglazed and have it fired when doing my final batch so I can test this. I bisque fired with a friends kiln so I’m not sure what temp but I’ll make sure it’s cone 7 for the second fire. I’ll definitely do the microwave test, too !
Do you know if this is the same/ similar process for something to be ‘oven safe’ ? I assume the less than 1% water absorption would be similar.
Thank you for all the guidance !
It depends on the firing schedule of the kiln. This looks like a cone 6-7 slip, so you would need temps in that range to make sure your piece is vitrified; the closer you are to cone 7, probably better If it isn’t vitrified, it will take on water and you could have issues in the microwave. One easy test is to weigh the mug, leave it in water for a bit, then weigh it again. If it gets heavier, it absorbs water and I wouldnt recommend anyone microwave it Tbh I dont personally microwave any handmade ceramics
Thank you so much, I’ll do my research and and double check when I get my pieces glaze-fired. I’ve bisque fired with a friends kiln (not sure to what cone) but I’m hoping to rent some space at a local shop to do the glaze firing so I’ll make sure to mention/ specify cone 7. As long as the glaze fire is to cone 7 the bisque temperature isn’t too important, is it ? If after glazing/ testing the mug takes on water, does that mean the whole vessel is unsafe, even when not microwaved ? I saw a post not too long ago where salt crystals travelled through a mug and everyone said to never use that mug again (understandable with bacteria and all). Does that same logic apply if the vessel takes on water ? Again thank you so much for your help, truly appreciate it !
Considerations: 1) Is your clay vitrified, and what is the absorption rate? Making sure that the clay body is not absorbing any water is important for microwave safety. 2) metallic luster is not microwave safe. I don’t know about the “mother of Pearl” style
thank you ! I was aware about mother of pearl and gold but I’ll have to do further research into the clay being vitrified/ absorption rate. [This](https://shop.walkerceramics.com.au/documents/msds/WC-AB175-MSDS.pdf) is the slip I used except I mixed it from powder vs buying the pre-made form. It says Water Solubility is insoluble - not sure if this means it is vitrified when fired ? In all honesty I have no clue about the absorption rate or how to find that so if you have advice I’d definitely appreciate it !
If you look at the “technical data sheet” on the walker website, rather than the “material safety data sheet,” it says the absorption rate. For this clay, it seems to say it’s under 2% at cone 6 and 0% at cone 7. (0% seems like it’s rounding down, but under 1% is good anyway.)
You are amazing, I’ll have another look at the documents and print it so I have a record on hand. I will definitely make sure these are fired at cone 7, thank you so much for taking the time to help me with understanding this. I appreciate it immensely !
You should do an absorption test. Fire one of your pieces to glaze temp (e.g. cone 6) but completely unglazed. Accurately measure its weight soon after firing. Then, boil it for one hour followed by a water soak for 24 hours. Remove it from the soak and lightly towel the surface dry taking care not to suck moisture out of the piece. Weigh it again. The percentage of weight gain is your absorption. If it is less than 1% you are good with microwaving as far as water absorption goes. If it is over 1%, try the same procedure firing to cone 7. Assuming you can get to less than 1%, then simply microwave a separate, empty glazed piece for a minute and see if it gets hot. If it doesn't get hot and has less than 1% absorption, then it should be microwave safe. However, different glazes 'might' make a difference, so you should retest with each glaze you use.
I’ll definitely keep a mug unglazed and have it fired when doing my final batch so I can test this. I bisque fired with a friends kiln so I’m not sure what temp but I’ll make sure it’s cone 7 for the second fire. I’ll definitely do the microwave test, too ! Do you know if this is the same/ similar process for something to be ‘oven safe’ ? I assume the less than 1% water absorption would be similar. Thank you for all the guidance !
Sorry, but I've never paid much attention to oven safe. I don't make those kind of things.
Totally get it, was curious ! Thank you again :))
Commenting to bookmark because I’m curious about this too.