Does Underglaze Stick to the Kiln Shelf? Avoid Melting Problems


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Does Underglaze stick to the kiln

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If you have made your first piece of pottery you may be wondering enthusiastically about how to finish it.  You may have heard that glazes melt and if you aren’t careful they can weld your pottery to the kiln.  Perhaps this has left you wondering does underglaze stick to the kiln shelf in the same way?  Don’t stress, just read on to find out how underglaze behaves when it is fired.

Normally underglaze does not stick to the kiln shelf when it is fired.  However, this depends on the kind of underglaze you are using and how you have applied it.  Most modern underglaze does contain silica, which melts when it is fired.  So, your underglaze may become a bit sticky.

Will Underglaze Stick to the Kiln? – Factors at Play:

Underglaze is used mainly for decorative purposes.  It can be applied to greenware or bisqueware.  Often it is fired once and then a clear glaze is applied on top of the fired underglaze.  However, if it is painted on bisqueware, then the glaze is applied to the unfired underglaze.

Two Relevant Differences Between Underglaze and Glaze:

When glaze melts in the kiln it creates a non-porous layer on ceramics. Modern underglaze does contain some ingredients that melt like a glaze

However, usually, it doesn’t contain sufficient of these to create a non-porous layer. Because underglaze does not melt as much as glaze, underglaze decoration tends to stay put when it is fired. 

By contrast, the colors and patterns in a glaze will tend to move about and change when it’s fired.  So, it’s harder to predict what a fired glaze will look like.

Does Underglaze Stick to The Kiln if it is Applied Poorly?

There are many ways to apply underglaze.  It is a very versatile medium and offers huge scope for creativity. 

However, one thing that is common to most underglaze techniques is that it tends to go on thinner than a glaze.  When you apply underglaze to pottery it evaporates and dries quite quickly.  Especially if it’s being applied to bone dry clay or bisqueware.

As such you will need at least 3 layers of underglaze for the colors to pop.  However, even when three layers have been applied the underglaze will still be a relatively thin coat.

Does underglaze stick to the kiln shelf

One of the reasons that glaze can stick to the kiln is that it can be applied quite thickly.  If it is put on too thick when it is fired it can run down the side of the pottery. 

You can end up with a piece of pottery that looks like Winnie the Pooh’s honey jar.  It will stick to the kiln where the glaze has run from the pot onto the shelf.

This is less likely to happen with underglaze.  Underglaze can be applied thicker than necessary and may drip.  However, this is not likely with most underglaze techniques.  You are much more likely to have a build-up of thinner layers. 

As well as having a thinner constitution than most glazes, the ingredients in underglaze melt less than a glaze.  Although most modern underglaze does contain silica, it is less than that of a glaze.  As such it is less likely to stick to your kiln shelf.

So, Does Underglaze Stick to the Kiln Shelf?

The answer is normally ‘no’.  However, if you’re using a new underglaze that you are not familiar with, it is best to proceed with caution. 

One tip is to do test pieces with a new underglaze. Use these to see how the underglaze responds in the kiln before using it on your pottery.

How to Prevent Underglaze From Sticking to the Kiln Shelf

Some things about firing underglaze are relatively predictable.  For example, if they are handled well, they tend not to bleed when they are fired. 

Also, their color after firing is usually the same color as they are in the pot.  This does depend on what temperature they are fired at, but generally, you can predict how they will turn out.          

However, whether the underglaze will stick to the kiln is less easy to predict, especially with an unfamiliar underglaze.

Tips to Prevent Underglaze Sticking…

  1. Use wax resist on the base of your pottery.  This is what potters use to prevent glaze from going onto the base of their pottery.  It helps them avoid the glaze melting onto the kiln. 

    You can use a similar technique with underglaze for the first few times you use it.  Once you are familiar with the underglaze you will get a better idea of whether wax resist is necessary. 

    It may be that you will be able to use the underglaze all over your pottery, but it’s best to proceed with caution to start with.
  2. Position your items in the kiln so that they are not touching one another.  Again, it might become apparent after a few fires that the underglaze won’t melt pottery onto other items.  But whilst you are road-testing it, keep your pieces separate.

  3. Use a kiln wash on the shelves.  Kiln wash is a liquid mixture that is applied to your kiln shelves.  It melts at very high temperatures.  It prevents glaze and underglaze from sticking to the kiln by creating a barrier between the glaze and your shelves.

  4. Another option is to use kiln stilts.  Kiln stilts are pieces of high-temperature wire, which are set into ceramic.  They act as small ledge or support for pottery to keep it off the kiln shelf.  They can only be used in low-temperature firing (up to 2000F), as the metal will melt above this point.

Some underglazes may stick a little, but it won’t be enough to cause any damage. Just be careful, read the brand’s instructions thoroughly, and do a test run so you’ll know for sure how your kiln and the underglaze will work together.

Final Thoughts

Does underglaze stick to the kiln is a sensible question to be asking when you are new to firing pottery.  The best way to approach this issue is to ask the right questions and study your particular brand of underglaze.  To sum up, as a general rule, underglaze will not stick.  However, the method you have used to apply it and the brand of underglaze may affect your results.

Sometimes, underglaze color transfers onto the bottom of the pot and, therefore, the kiln shelf itself.  At other times you will get away with stacking items that have been underglazed.

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