Stoneware Bottle Cork Problem

[k.mammasis]

Dear all,

 

We are facing a problem with our stoneware bottle and I would like to receive your comments and thoughts on this important issue.

 

Our bottle is made from stoneware and as a result our bottleneck varies. We have been trying to keep the diameter of the bottleneck as constant as possible, approximately 20mm. However, due to the bottle entering the firing process the bottle contracts and resultantly we have alternations in the final bottleneck dimensions. Unfortunately, this generates another problem that relates to the cork itself and the type of cork to be used. It seems that we are trapped into using only a natural cork solution that can adapt to those variations. Typically, if the diameter of the bottleneck is 20 mm the cork's diameter should be 21mm. My potter tells me that there is nothing we can do to get a perfect bottleneck size at 20mm and it seems that the natural cork is the only solution.

 

I would really like to hear your thoughts on this problem.

 

Thank you very much.

 

Kindest Regards,

 

Konstantinos 

[neilestrick]

Assuming your firings are relatively consistent, your clay will shrink at the same % every time. You need to figure out the shrinkage rate of your clay and calculate what the wet size of the opening needs to be in order to achieve the fired size you need. You can make a simple tool/jig out of wood or plastic or even an old credit card to measure the opening of the bottle when throwing it.

[Callie Beller Diesel]

You can grind down rubber lab stoppers, and even polish them so they don't show the burrs. It's a bit more work, but it is doable. Even lab glass varies slightly.

But it would still be good to figure your shrinkage.

[Min]

The other way you could do it to ensure all the collars are exactly the same would be to make a collar mould. Like the ones for lotion pumps in the link below, once you have the mould prototype figured out they would be fast. Plaster for the mould then press in soft clay and attach to the bottles when leatherhard.

 

http://www.onedreamdesign.com/shop/index.php?main_page=product_info&products_id=181

[Pres]

Instead of the collar mold, you could get a tapered grinding wheel that met you diameter specifications, then have the bottles thrown with a thicker neck, after bisque use a drill press and grinder to open the neck to the diameter you need with just a little extra. Then after glaze firing, the shrinkage, and the glaze thickness which should be minimal would be accounted for. Most of the shrinkage would occur during the bisque fire.

[neilestrick]

Pres mentioned glaze thickness, which can definitely be an issue with corks fitting. I make oil bottles where I leave the inside of the neck unglazed so the cork gets a good grip. If I accidentally leave it glazed, the cork will not fit properly. Glaze takes up more space then you might think.

[k.mammasis]

Thank you all very much for your prompt replies, that have been really helpful.

[Mark C.]

If you want it the same every time slip cast it and make sure the glaze is the same every time as to application and thickness. This is no small task.

Mark

[ronfire]

just make a taped dowel or larger stopper that will fit into the thrown bottle to size it to the dimension required before shrinkage. They should all be the same then.