|a brief introduction to glass and gems||or look at polishers and tumblers at electrictumblers.co.uk|
Glass is used to make things such as beads, bottles, electronic components, insulators, jars, light bulbs, mirrors, optical instruments, ornaments, tableware, windows, and vases. It's inexpensive and versatile and can be used at a basic level with very little skill.
A gemstone, also called a crystal, diamond, jewel, or precious stone, is a piece of mineral cut and polished to make jewellery or other adornments. Some rocks such as lapis lazuli and opal, and organic materials such as amber, jet, and pearl, are often casually called gems. Most gems are hard, but softer minerals are also used because of their lustre or other physical properties that have aesthetic value.
A BRIEF INTRODUCTION TO GLASS AND GEMS
The main component of glass is silicon dioxide, often called silica: found naturally and plentifully as sand. When it melts, at around 1700°C, it's like syrup on a cold day. When it cools, it forms a rigid brittle glass called quartz glass.
To lower the melting point, and reduce the cost of melting, chemicals are added: typically sodium carbonate and calcium oxide. Other chemicals, and different heating and cooling processes, produce a range of colours and mechanical properties.
Chemically, glass is defined as an amorphous solid but, as it's heated, it becomes softer allowing it to be blown, cast, coated, decorated, engraved, heat-treated, moulded, poured, pressed, sagged, and slumped.
A form of glass occurs naturally within the mouth of a volcano when the intense heat of an eruption melts sand to form Obsidian, a hard black-to-brown glassy type of stone, shown in the photo. Although it was used decoratively, when it fractures it has very sharp edges, many times sharper than a steel knife-edge, so was also used for tools and weapons: and the pitiful rituals of circumcision and female genital mutilation.
During annealing, fabrication stresses are relieved as the molecules cool and arrange themselves into a regular stable matrix. Successful annealing is the key to creating glasswork that will remain attractive and durable. It's quite a long process, so a kiln with an automatic comprehensive programmer is essential.
|FREE BEAD ANNEALING GUIDE|
You can download, and print, a Bead Annealing Guide. Paragon created it in 2013 so it's only a guide, not a contemporary definitive document. Click here. It's a pdf file, but your device should already have a pdf viewer.
Cubic Zirconia is the most popular substitute for a diamond because they look almost dentical. Cubic Zirconia or CZ, is made from zirconium dioxide which comes closer than any other gem to matching the characteristics of a diamond. It's not quite as hard as diamond and is slightly less sparkly but displays more prismatic fire with more colour sparkles within the gem, especially if metal oxides are added during the production process.
Caring for CZ is important because they are more brittle than diamonds and susceptible to wear and tear such as chipping and scratches over time.
Diamonds are not a form of glass: they're naturally occurring gems composed of carbon atoms arranged in a very regular pattern.
Between 1 billion to 3.3 billion years ago, simple carbon containing trace minerals was transformed into diamonds by heat and pressure at depths of over 100 miles below the earth’s surface. We can’t mine down far enough to reach the earth’s mantle but fortunately volcanic eruptions brought the diamonds closer to the surface. They're extremely hard and until recently were regarded as the world's hardest natural material.
Although diamonds are extremely expensive, their price is governed by carat, cut, colour, and clarity. It’s very rare to find a diamond that doesn’t contain flaws: however the impurities, and internal refraction and dispersion of light, give diamonds their brilliance.
Synthetic diamonds are manufactured and are identical in hardness, dispersion, gravity, refraction and chemical composition to the highest quality mined diamonds available. Whereas a one-carat top quality diamond would cost thousands of pounds to buy, the same quality man-made diamond could be made for less than £5.
This will obviously have a huge impact on the diamond industry over the next few years as when comparing a cultured and mined diamond side by side they are virtually undistinguishable. A bit like pearls, they can be grown from a single crystal using chemical vapor deposition.
Dichroic glass has two different colours: a transmitted colour and a reflective colour, both of which change depending on the angle of view. For example blue-red will be blue in transmission and red in reflection.
During manufacture, quartz and metal oxides are vapourised onto the surface of the glass using a vacuum deposition process, forming a multi-layer crystal structure.
Enamelling involves applying a glass paste to metal and then heating it to fuse it to the surface. The finish of the enamel can be translucent or opaque depending on the temperature used to melt the glass. Higher temperatures result in a more transparent and durable enamel whilst lower temperatures give a more opaque and fragile surface. Dyes and pigments can be included to produce any colour.
The Paragon SC2 is ideal for enamelling, although other kilns are fine. So click the sc2-sc3:jewellery link below the menu bar near the top of the page. The SC-2W and SC-3W doors include a 50mm x 50mm heat-resistant glass viewing-window in the centre of the door, allowing you to take a quick peep at china paints, enamels, glass, and glazes to check on their progress
To fire polish glass, return the items to the kiln and melt them just enough to give a smooth polished appearance. It needs a temperature of around 700°C, and is often used to round the edges of glass after fusing.
Fire polishing already-slumped items is more difficult because the polishing temperature is close to the slumping temperature and it can distort the appearance of the piece. So it generally works best for flat items, rather than slumped ones. It has the slight limitation that the part of the item that touches the kiln shelf won't polish.
|FUSING, SAGGING, AND SLUMPING|
If two or more pieces of glass in contact are heated, they begin to soften and fuse together. With careful heating and cooling, the separate pieces of glass become one.
If glass is put on a mould and heated, it begins to soften and collapse, or sag, onto the mould: a common technique for making bowls and plates.
Sagging and slumping are often thought of as being the same. Correctly: during sagging, heated glass, supported at its edges, sags down in the middle to conform to a mould; during slumping, heated glass, supported at its middle, slumps down at its edges to conform to a mould.
|LAMPWORK AND BEADS|
Lamp-working is the traditional name for glasswork that uses a flame to melt glass rods and tubes. As the glass softens, it's shaped by turning and using tools.
Early lampworkers used an oil-lamp, and blew air into the flame through a pipe. Later, propane, natural gas, or butane torches replaced the lamp, although kilns are now increasingly popular, particularly for annealing.
Beads are usually made on steel rods, or mandrels. When the beads are finished, the rods are removed leaving holes for threading the beads. Cold working techniques can be used, such as etching, faceting, polishing, and sandblasting.
Lost-wax burnout starts with making a wax shape and then making a mould of the shape. When the mould is heated in a kiln, the wax melts out through channels, usually over a burnout mesh and into a tray. The shape is then cast in glass or metal from the mould.
It's important to prevent wax or carbon sticking to the elements, so burnout kilns have a top vent to release fumes. Carbon build-up inside a kiln could conduct electricity and would eventually cause the elements to fail.
Paragon make kilns designed for this: the W series. So click the w:lost-wax link under the menu bar near the top of the page. They all have top vents and optional wax trays.
Moissanite is another diamond substitute which is a rare mineral found naturally in small quantities, although Moissanite for jewellery is artificially made. It’s made from Silicon Carbide which means it’s able to withstand high temperatures and is very hard.
Moissanite is noticeably much sparklier and displays more prismatic fire than a diamond which is noticeable even to an untrained observer. Moissanite does have inclusions like a diamond and it may also have a greenish tinge to its colour.
|PÂTE DE VERRE|
Pâte de verre involves making a glass paste, applying it to a mould, firing it, and removing the piece from the mould. The glass paste is usually made from glass powder, a binder such as gum arabic, distilled water, and colouring agents or enamels. It allows precise placing of colours in the mould, whereas other techniques often result in the glass straying from its intended position.
I think, currently, Daum is the only large commercial crystal manufacturer using the pâte de verre process for art glass and crystal sculptures.
This a simple technique but it requires good ideas. A bottle, such as those used for wine, beer, cola, or champagne, is softened in a kiln so that it begins to flatten out or conforms to a mould. There are too many moulds to stock here but there are lots available on line. Or make your own from clay.
The bottles need to be clean and dry, with all paper labels and tops removed. Put them in your kiln on a shelf, either with shelf paper or kiln wash to prevent the glass sticking to the shelf.
Paragon makes a kiln designed for this: the Trio. So click the trio link below the menu bar near the top of the page. It's wide enough for most bottles but can still use a regular socket.
Stained glass is glass that has been coloured by adding metallic salts during its manufacture. The coloured glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures, traditionally held together by strips of lead and supported by a rigid frame. Painted details and yellow stain are often used to enhance the design.
The term stained glass is also applied to windows in which the colours have been painted onto the glass and then fused to the glass in a kiln.
It requires artistic skill to conceive an appropriate and workable design, and engineering skills to assemble the piece. A window must fit snugly into the space for which it is made, must resist wind and rain, and also, especially in the larger windows, must support its own weight. Many large windows have withstood the test of time and remained substantially intact since the Late Middle Ages.
Swarovski Crystal isn’t a gemstone or even a crystal: it’s a form of glass made at high temperatures by melting silicon oxide powders with lead to form what is known as lead crystal. The exact process is patented by Swarovski but it has approximately 32% lead content to increase the crystals refraction index to resemble that of a diamond. To produce a diamond like effect the crystal glass is precision cut and then polished again by a Swarovski patented process that gives the crystal a high quality finish.
The crystals are often further enhanced by coating the glass with an Aurora Borealis or AB coating that gives the surface a rainbow like appearance to simulate dispersion from a diamond. Swarovski crystal is not as hard as diamond so its susceptible to scratches and chipping from wear and tear, but it’s harder than standard glass.
Tack fusing is the joining together of glass, with as little change to the shape of the pieces as possible. Tack fusing may be used either decoratively, or to assemble a large piece of glass from laminations.
Where tack fusing is used to apply small decorative details to a larger piece, you might want to partially melt the small pieces so that they change shape, usually becoming more spherical under the influence of surface tension, but without changing the shape of the carrier piece. This can be done by using an increased temperature, but only briefly. The carrier piece has a larger thermal mass, so heats up more slowly than the small decorations.
The vitrigraph process usually uses a kiln to make glass stringers. The bottom of the kiln is removed and set aside. The kiln body is put on a thick ceramic square with a central hole.
A crucible of glass is put inside, and the whole combination lifted well away from the floor to allow moulten glass to fall through a hole in the crucible and form long stringers. Ceramic squares are in the on-line shop.
Paragon make a kiln designed for this: the Caldera. So click the caldera:ceramics link below the menu bar near the top of the page. The bottom is a separate part and can be unclipped.
The term warm glass refers to fusing, slumping, and other glass processes which take place at temperatures between about 600°C to 925°C. Although that doesn't sound warm, it is when you compare it to glassblower's working temperatures, which often exceed 1100°C. Warm glass is sometimes called kiln-formed glass.