Heavy Metals in Glass

Some concern has been expressed about the metals used in colouring glass.  This centres around the temperatures used in fusing and whether kiln workers may be of risk from these heavy metals vaporising.

First of all, let’s get some sense of perspective. This is from Greg Rawles, an acknowledged expert on the hazards of working with glass.

Understanding Exposure:

In reality, unless you are doing:
High-volume production work that exposes you to a health hazard all day long
You are exposing yourself to high levels of a health hazard for a brief time
You are working with a very toxic material
You are not working responsibly

You are not really at risk for an unacceptable exposure when working in a glass studio  http://www.gregorieglass.com/chemicals.html

Now, let’s think about how likely it is to have heavy metals vaporise at kiln forming temperatures. How stable would glass be if the metals that colour it vaporised when we fired it? the colour would vary with the heat and number of times we fired it.

Now, let’s think about how likely it is to have heavy metals vaporise at kiln forming temperatures. How stable would glass be if the metals that colour it vaporised when we fired it? the colour would vary with the heat and number of times we fired it.

Even if the metal were to evaporate, how much is in the glass. Apparently, Bullseye uses less than 3 pounds of cadmium for a pot of glass. We can tell from the sheet numbers that a pot of glass gives at least 2000 sheets of glass, so there is ca. 0.0015 lbs or .07 grams or less of metal in a sheet of 3mm glass. There is very little there to "vaporise", so even it were able to evaporate, it is in such small quantities as to be negligible, and the exposure so low as to be of extremely low risk. There is however, no risk in protecting yourself with dust masks. Just remember that the risks from vaporised heavy metals is much less than most of the other studio practices involving glass. If you need breathing protection for metals (and you may feel it is not worth the risk) then you need to be wearing a mask all the while you are doing glass work. It is about relative risk.

For complete information, the melting and boiling points of various metals relevant to glass colouring are given below.  The vaporisation will be somewhere above the melting point and toward the boiling point.  You will be able to see the relevant temperatures and take any precautions you feel are necessary.  Remember that the metals are not used in their pure forms, but as oxides.  These may have different melting and boiling temperatures.  In general, the oxides used in colouring glass have higher melting and boiling points than the pure metal.

Antimony -for whites

Melting point: 630C

Boiling point:  1635C

Antimony Oxide

Melting point:  380-930C

Boiling point:  1425C

Cadmium 

Melting point: 321C

Boiling point:  767C

Cadmium sulphide - yellow

Melting point: 1650-1830C

Boiling point:  2838C

Chromium 

Melting point: 1907C

Boiling point:  2671C

Chromic Oxide – for emerald green

Melting point: 4415C

Boiling point:  7230C

Cobalt 

Melting point: 1495C

Boiling point:  2927C

Cobalt Oxide- blue to violet

Melting point: 1900C

Copper 

Melting point: 1084C

Boiling point:  2562

Copper Oxides - for blue, green, red

Melting point: 1232-1326C

Boiling point:  1800-2000C

Gold

Melting point: 1337C

Boiling point:  2970C

Gold Chloride - red

Melting point: 170-254C

Boiling point:  298C

Iron

Melting point: 1538C

Boiling point:  2862C

Iron Oxide – for greens and brown

Melting point: 1377-1539C

Boiling point:  3414C

Lead – for yellows

Melting point: 327C

Boiling point:  1749C

Manganese 

Melting point: 1246C

Boiling point:  2061C

Manganese Dioxide – purple and a clarifying agent

Melting point: 535-888C

Neodymium

Melting point: 1024C

Boiling point:  3074C

Nickel 

Melting point: 1455C

Boiling point:  2730C

Nickel Oxide – for violet

Melting point (II - for green): 1955C

Melting point (III - for black): 600C

Selenium

Melting point: 221C

Boiling point:  685C

Selenium Oxide – for reds

Melting point: 118-340C

Boiling point:  350C

Silver 

Melting point: 961C

Boiling point:  2162C

Sodium

Melting point:  370C

Boiling point:   882C

Sodium Nitrate – a clarifying agent

Melting point: 308C

Boiling point:  380C

Sulphur

Melting point: 115C

Boiling point:  444C

Sulphur oxide - for yellow to amber

Melting point:  17C

Boiling point:   45C

Tin 

Melting point: 231C

Boiling point:  2602C

Tin Oxides – for whites

Melting point:  1080-1630C

Boiling point:  1800-1900C

Uranium

Melting point: 1132C

Boiling point:  4131C

Uranium oxide – for fluorescent yellow, green

Melting point:  1150-2765C

Boiling point:  1300C

Colour “theory”

You will need to decide which colours combine well, whether they are toning, harmonious or complimentary.  By getting to grips with the rules of colour, you can give your work a unity of concept.

Primary colours

Primary colours are three key colours - red, blue and yellow. They cannot be made from any other colour.

Secondary colours

If you mix equal amounts of the primary colours, you get the secondary colours - purple, green and orange.

red + yellow = orange
red + blue = purple
blue + yellow = green

Tertiary colours

If you mix a primary with a secondary colour, in a ratio of 2:1, you get a tertiary colour. red-orange, blue-green etc.

Colour wheel example

Cool versus hot

Look at the colour wheel and you will see the left hand side of the colours are 'warm' or 'hot' and the ones on the right are 'cool' or 'cold'. This is useful when you want to create a mood in a particular room or need to make your space cosier or lighter.

Neutrals

Neutrals are one of the easiest groups of colours, or non-colours to work with. They don't appear on the colour wheel and include Black, Grey, White and sometimes Brown and Beige. They all go together and can be layered and mixed and matched. No neutral colour will try to dominate over another.

Accent colours

An accent colour is a colour used in quite small quantities to lift or to add punch to a colour scheme. An accent colour should be in a complementary colour. It works best if it's a bright, vibrant colour. Accent colours are perfect if you're concerned about using strong colour - simply add a splash of an accent colour. Keep most of your piece in shades and variations of one single harmonious colour. Then pick out just a few objects in an accent colour.

Clashing colours

Using clashing colours is thought to be inappropriate in formal settings. But in other settings they can provide drama, if they are used carefully. If they are of equal tonal strength, you can mix them together. You don't have to stop at two, you can try three or four. But if one is paler or weaker than the rest it will get lost in the overall scheme.

Design Sources

Principles of design practice for stained glass, 4

Use the everyday visual experience and make interpretations and adaptations. E.g.,

• draw lead lines on an illustration to make it suitable for stained glass, using the fewest lines possible
• Use your photographs of interesting subjects and scenes

These may never become useable designs or cartoons, but will increase you abilities to design from the real world toward the abstract.

Make and keep sketches as personal references. These do not need to be finished drawings, just a reminder of the thing(s) that caught your eye. Many artists always carry around a notebook to record these observations. Even if you only make drawings on paper napkins, make a folder to keep these separate sketches together.

Take photos of shapes and interesting images. These can then be used later to develop images.

Make up composite images by using overlays or collage. This helps develop your compositional abilities.

Work on abstraction in your design practice:

• Study abstract representations. Dissect – decomposition is a popular word - and analyse how the work is put together.
• Use geometric design as an introduction to abstract design. This forces your attention to structure, balance and colour.
• Once the distribution of the physical and visual weights is understood, this enables the jump to more free forms of abstraction.

Elements of Design:

Designing for strength 

Colour selection

Design lines 

Design sources 

Reworking designs 

Responsive Colour Selection

Principles of design practice for stained glass, 2

The graphic form of much stained glass means that the medium is about line and colour. This requires that you think about both your and the viewer's response to the colour combinations. Respond to your instincts. Use you feelings about colour and their relationships. Try different colour ways. Formal training does help, but experience develops your skills. The individuality of the piece depends on the use of your instincts about the colour. There are some checks you can make while selecting colours.

Think of colour and impact. Hot colours tend to have more impact, as they give bright points or areas. Impact can also be created by using non-complementary colours together. If a more subtle impression is desired, use tonal variations without great contrasts.

Vary areas of colour and their proportions. This provides interest to a panel. It avoids a mechanical symmetrical appearance, even if the design is symmetrical

Think about colour balance. Although the colours may vary it is important that the weights of the colours are balanced so that the focus of the panel is not taken to another part because of the imbalance of the colour with the design.

When you are in difficulty selecting or arranging the colour, step back and view from a distance. This is one of several techniques to enable you to get a larger or different view. Others include viewing the design through a mirror, viewing through half closed eyes, look at the design from the other end, and viewing the design from acute angles.

When something feels wrong, trust your intuition and use other colours. Colour theory is just that -theory. It is through using your reactions that the piece becomes individual.

Seek out the nuances of the glass in tones and textures. These alter the perceived colour and weight considerably.

Keep the design lines simple when your emphasis is on colour, light and texture. This allows those qualities to dominate the panel, rather than the lines.

Always make a coloured drawing, before choosing the glass, as a reference. This is a rendering of your original idea. It provides a reference as you select the colours. It is something that can be altered, of course, but does provide an essential reference point.

Choose glass colours in the kind of light for which the panel is intended. This is essential, as the glass colour is subtly different in daylight, incandescent, and fluorescent lights.

Elements of Design:

Designing for strength 

Colour selection

Design lines 

Design sources 

Reworking designs 

Choosing Glass for a Harmonious Appearance, 3

Different colours, of course, have different appearances. The most commonly known one is the hot/cool colour combinations. This still applies when dealing with opalescent glasses, where reflection is the dominant experience of the colour.

But in glass where there is quite a bit of light transmission, the receding and advancing colours are not exactly the same as in painting and opalescent glass. The greatest separation comes with intense red (close) and intense blue (distant). In some circumstances these can be experienced as apparently being in different planes.

There are a few distinct advancing and receding colours, but most are much more subtle and are not all as expected from the experience of reflected colour. Clear, for example appears nearer than a strong blue. It is up to each person as to how far they wish to take these combinations.

Those who do want to investigate, should go to a place where they can view windows with small pieces and a variety of colour in strong light. They can then record which colours appear to “float” above others, or recede.

Choosing Glass for a Harmonious Appearance, 2

Clarity of colour

When considering the representation of distance or depth you need to look for glass that is less pure. The colours that are muted or have a touch of white, blue or grey will provide a good representation of distance. The pure colours will appear more brilliant among the more muted colours.

This is where glass samples can be most useful. By holding them up to the light, you can see the effects one glass has on another and how one colour will appear among the others.

Choosing Glass for a Harmonious Appearance - 1

There are at least two major elements in choosing glass: density and clarity. A third is the “hot/cool” effect of colours. The appropriate combination of these elements leads to a panel with bright or hot spots where you want them. You can create a dramatic image or a more restrained one with more gradual gradations of light without obvious bright or dark areas.

Density

Density relates to the amount of light the glass allows through. Clearly black is the most dense glass – allowing no light through. In general, glass can be divided into opalescent and transparent.

Opalescent glasses range from the very dense opaque to less dense translucent glass.

Transparent glasses have a variety of densities too, although almost always less dense than opalescent glass. The density of transparent glasses relates to the intensity of the colour and the texture of the glass.


Colour intensity

The intensity of the colour is related to the amount of light allowed through. The intensity is directly related to the saturation of the colour. A further effect on colour intensity is the thickness of the glass. If you look at a handmade sheet of glass with different thickness on one end to another end, you can see the gradation of the colour and the amount of light that comes through.

Glass Textures

The texture of the glass affects the density of the glass. A smooth glass will have less density as the light passes through without dispersion. As the glass becomes more textured, the light is more dispersed and so appears more dense.

Colour combinations

You will need to decide which colours combine well, whether they are toning, harmonious or complimentary. By getting to grips with the rules of colour, you can give your work a professional look.

Primary colours
Primary colours are three key colours - Red, Blue and Yellow. They cannot be made from any other colour.

Secondary colours
If you mix equal amounts of the primary colours, you get the Secondary colours - Purple, Green and Orange.
Red + Yellow = Orange; Red + Blue = Purple; Blue + Yellow = Green

Tertiary colours
If you mix a primary with a secondary colour, in a ratio of 2:1, you get a Tertiary colour. Red-Orange, Blue-Green etc.

Cool versus hot
Look at a colour wheel and you will see the left hand side of the colours are 'warm' or 'hot' and the ones on the right are 'cool' or 'cold'. This is useful when you want to create a mood in a particular room or need to make your space cosier or lighter.

Neutrals
Neutrals are one of the easiest groups of colours, or non-colours to work with. They don't appear on the colour wheel and include Black, Grey, White and sometimes Brown and Beige. They all go together and can be layered and mixed and matched. No neutral colour will try to dominate over another.

Except for the blue, these are examples of neutral colours

Accent colours
An accent colour is a colour used in quite small quantities to lift or to add punch to a colour scheme. An accent colour should be in a complimentary colour. It works best if it's a bright, vibrant colour. Accent colours are perfect if you're scared of using strong colour - simply add a splash of an accent colour. Keep most of your piece in shades and variations of one single harmonious colour. Then pick out just a few objects in an accent colour.

Clashing colours
To use clashing colours is thought to be a no-no in formal settings. But in more informal or vibrant settings they can look fantastic, if they are used carefully. If they are of equal tonal strength, you can mix them together. Don't stop at two, you could try three or four. But if one is paler or weaker than the rest it will get lost in the overall scheme.