Cleaning Materials and Solutions

You need to clean glass that is going into the kiln to avoid devitrification on the surfaces.  This can be a greater or lesser problem for different individuals.  It is probably related to the studio practice and the amount of oils in or on fingers.

The first things to consider in cleaning glass for kilnforming are what you are trying to eliminate from the glass, the chemical nature of glass, and how to avoid putting further contaminants on the glass.

Cleaning is to remove surface deposits

The sensitivity of glass to minor contamination is shown by the fact that the small amount of oil from your finger tips can provide sources of devitrification.  This means the glass needs to be really clean and free from any deposits.  You need to remove oils and dusts and anything you may have added during assembly to leave nucleation points for devitrification. This includes any minerals in the water used to clean the glass.

Avoid soaking in acids

Glass is an alkaline (or basic) material.  This means that acids can affect the surface of the glass – at the microscopic level – enough to provide those nucleation points for devitrification to develop.  An odd thing about the way vinegar attacks glass is that the more dilute it is, the more etching it does of the glass.  This has to do with the greater amount of oxygen to transfer from the vinegar water to the glass, leaving microscopic etching as the minerals encased in silica are released from the glass surface.  This is visible as mild dulling in the shine of the surface.

If acids are used to clean the glass, rinse immediately in an alkaline solution such as baking soda.  You need then to get rid of the chemical reaction products formed by the neutralisation of the acid.  This should be done by immediately rinsing with running clear water. Follow this with a polish dry using unprinted paper towels.

Cleaning with spirits

My recommendation is to avoid spirits, especially those with additives such as rubbing alcohol. The amount of oil that is to be removed from the glass is small, so application of large amounts of spirits is not necessary.  It is reported that some aggressive spirits may affect the surface of the glass by combining with the minerals or the silica of the glass – this is not proven. If you do use spirits make sure they are thoroughly cleaned off and polished dry.  It is all too easy to leave residues.

What can I use to clean the glass?

The simplest cleaner is water.  A drop or two of dish washing liquid can provide a break to the surface tension, allowing the water to flow smoothly over the whole surface.  Then polish dry with clean unprinted paper towels.  Often this will not be sufficient to clean all the oils and chemicals from the glass and the best alternative is to use isopropyl alcohol neat or diluted 1:1 with water.

In many areas, the public water supply is hard – i.e., has an appreciable level of minerals.  Calcium and iron are two common minerals in any water supply. Some water supplies have other additives such as chlorine, fluorine and other purifiers. Chlorine and fluorine react strongly with glass, so air drying is not a good choice in drying glass in areas where there are these chemicals in the water supply.  Iron is another strong reactor with glass.  In high iron areas it may make it difficult to use water as the cleaning element.

It is suggested that distilled water can be used instead of the public water supply.  Yes, it can.  But it is expensive and not necessary.  Instead there are a few commercial cleaning agents that work well.  In North America Spartan glass cleaner is recommended.  In Europe Bohle glass cleaner is recommended.  I use isopropyl alcohol as my final rinse.  

After applying these glass cleaners, you still must polish to squeaky clean and dry.

Revised 28.12.24