Wednesday, 14 October 2015

Kiln Forming Myths 6

Big thin bubbles are art

Unless you have designed the bubbles, they are mistakes, not art.  Even when designed, they are delicate and when broken are very sharp.  So, they cannot be sold or used as they are even by yourself. 

Bubbles within the glass in a plate.

People frequently make the suggestion that the bubble should be broken and the cavity filled with frit.  Of course this can be done, but almost always appears a fix rather than a design choice.

The more important thing is to learn the cause so it can be prevented in the future.  Bubbles can be between layers or from underneath the whole piece.

Bubbles between the layers of glass are usually the result of inclusions or layup and firing rates.  Anything which holds the upper layer above the lower one has the potential to induce bubbles.  Most often, with a bubble squeeze, these are relatively small and are 2mm or more thick.  These may be acceptable or seen to be unsightly, but are not dangerous.  The bubbles can become large and/or thin with high temperatures or fast rises in temperature.  Be sure to have a good bubble squeeze, and a moderate (ca. 300°C) rise in temperature from there.

Bubbles can also rise between the shelf and the glass.  This happens most often when firing single layers above a low temperature tack fuse.

A single layer piece with large, burst, healed and emerging bubbles.

It can also occur when there is either debris between the glass and shelf, or when there is a depression in the shelf.  Both these cases allow air to remain trapped between the shelf and the glass.  Slower rates of advance and bubble squeezes can help reduce these, but the shelf needs to be checked for debris and high or low spots.

The piece below is disfigured by the random bubbles at the left and in the centre of an otherwise acceptable platter.

Evaluate your pieces before you declare a single or series of large thin bubbles art.  Of course, you should play around with the piece to learn from the mishap.  You can use the pieces of it in other projects.  But unless it is truly exceptional, it is a mistake, not art.

All myths have an element of truth in them otherwise they would not persist.

They also persist because people listen to the “rules” rather than thinking about the principles and applying them.  It is when you understand the principles that you can successfully break the “rules”.