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Glasses

Optical glass is used for optical instruments, such as binoculars, spectacles, lenses, prisms, telescopes, and microscopes. It must be absolutely flawless, completely transparent and able to be ground into shape. Of all glass types, it has the widest range of compositions, each having slightly different ingredients and optical properties. During the Second World War, the Optical Munitions Panel recommended that six types of optical glass should be made in Australia: Hard Crown; Dense Flint; Borosilicate Crown; Extra Dense Flint; Medium Barium Crown; and Telescope Flint. The production of optical glass requires special ingredients, in particular a high grade, iron-free source of silica (sand). Aeolian sand is considered one of the best types of sand for making optical glass and, fortunately, Australia had a domestic source of this essential ingredient at Botany, in Sydney. Other ingredients required for optical glass came from various Australian states: calcite (for lime or calcium oxide) - George's Plains (near Bathurst, New South Wales); zinc oxide - Tasmania; lead oxide - Port Pirie, South Australia; and soda ash - Imperial Chemical Industries' plant at Osborne, South Australia. The remaining ingredients were supplied by the UK (potassium nitrate and hydrated alumina) and the USA (borax and boric acid) and had been stockpiled by Australian Consolidated Industries before war broke out. (1) However, while Australia had all the ingredients to make optical glass, we did not have the procedures in place to do so. Optical glass is hard to form and expensive to produce; extraordinarily high temperatures are required to melt the quartz sands and these temperature make the mixture highly reactive. This can lead to contamination of the mixture through chemical reactions with containers that hold the molten glass. Optical glass is also a very viscous product, and it is difficult to get tiny bubbles out of the mixture. To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

The production of optical glass requires special ingredients, in particular a high grade, iron-free source of silica (sand). Aeolian sand is considered one of the best types of sand for making optical glass and, fortunately, Australia had a domestic source of this essential ingredient at Botany, in Sydney. Other ingredients required for optical glass came from various Australian states: calcite (for lime or calcium oxide) - George's Plains (near Bathurst, New South Wales); zinc oxide - Tasmania; lead oxide - Port Pirie, South Australia; and soda ash - Imperial Chemical Industries' plant at Osborne, South Australia. The remaining ingredients were supplied by the UK (potassium nitrate and hydrated alumina) and the USA (borax and boric acid) and had been stockpiled by Australian Consolidated Industries before war broke out. (1) However, while Australia had all the ingredients to make optical glass, we did not have the procedures in place to do so. Optical glass is hard to form and expensive to produce; extraordinarily high temperatures are required to melt the quartz sands and these temperature make the mixture highly reactive. This can lead to contamination of the mixture through chemical reactions with containers that hold the molten glass. Optical glass is also a very viscous product, and it is difficult to get tiny bubbles out of the mixture. To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

Stainedglass

Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

Fused silica

After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

To use the lens, first make sure the specimen is in focus under the high power (40X) objective. Next, move the high power objective out of position, place a small drop of oil on top of the cover slip above the specimen to be viewed and move the oil immersion lens into place. Use the fine adjustment knob to bring the specimen into focus. When you are finished, make sure to clean the lens and slide with lens paper. Also, it is extremely important that this oil does not contact any of the other objectives. If this should happen, clean the lenses immediately!

Edmund

Lead crystalglass

Although your microscope may differ in some details from the one described in the web page above, most microscopes will have one or more of the following objective lenses. You should acquaint yourself with each of these objectives and their uses.

However, while Australia had all the ingredients to make optical glass, we did not have the procedures in place to do so. Optical glass is hard to form and expensive to produce; extraordinarily high temperatures are required to melt the quartz sands and these temperature make the mixture highly reactive. This can lead to contamination of the mixture through chemical reactions with containers that hold the molten glass. Optical glass is also a very viscous product, and it is difficult to get tiny bubbles out of the mixture. To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

Other ingredients required for optical glass came from various Australian states: calcite (for lime or calcium oxide) - George's Plains (near Bathurst, New South Wales); zinc oxide - Tasmania; lead oxide - Port Pirie, South Australia; and soda ash - Imperial Chemical Industries' plant at Osborne, South Australia. The remaining ingredients were supplied by the UK (potassium nitrate and hydrated alumina) and the USA (borax and boric acid) and had been stockpiled by Australian Consolidated Industries before war broke out. (1) However, while Australia had all the ingredients to make optical glass, we did not have the procedures in place to do so. Optical glass is hard to form and expensive to produce; extraordinarily high temperatures are required to melt the quartz sands and these temperature make the mixture highly reactive. This can lead to contamination of the mixture through chemical reactions with containers that hold the molten glass. Optical glass is also a very viscous product, and it is difficult to get tiny bubbles out of the mixture. To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

Scanning Objective (4X): This shortest objective is useful for getting an overview of the slide (especially handy with some of the slides that contain whole organs like a section of the spinal cord, lung, digestive tract, ovary, etc.).

Optical prism

Crownglass

Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

Oil Immersion Objective (100X): This longest objective is used for observing the detail of individual cells such as white blood cells, the cells involved in spermatogenesis, etc. The lens must be used with a specially formulated oil that creates a bridge between the tip of the objective and the cover slip. Since the refractive indices of air and this lens are different, the lens will not work without this special oil!

Borosilicateglass

Low Power Objective (10X): This next shortest objective is probably the most useful lens for viewing slides. Almost any feature you need to observe in this course can be located with the 100X total magnification this objective provides. As an added benefit, the low power objective is always safe to use as it cannot be lowered to the point of contacting and thus possible breaking a slide. This is also true of the scanning objective mentioned above.

During the Second World War, the Optical Munitions Panel recommended that six types of optical glass should be made in Australia: Hard Crown; Dense Flint; Borosilicate Crown; Extra Dense Flint; Medium Barium Crown; and Telescope Flint. The production of optical glass requires special ingredients, in particular a high grade, iron-free source of silica (sand). Aeolian sand is considered one of the best types of sand for making optical glass and, fortunately, Australia had a domestic source of this essential ingredient at Botany, in Sydney. Other ingredients required for optical glass came from various Australian states: calcite (for lime or calcium oxide) - George's Plains (near Bathurst, New South Wales); zinc oxide - Tasmania; lead oxide - Port Pirie, South Australia; and soda ash - Imperial Chemical Industries' plant at Osborne, South Australia. The remaining ingredients were supplied by the UK (potassium nitrate and hydrated alumina) and the USA (borax and boric acid) and had been stockpiled by Australian Consolidated Industries before war broke out. (1) However, while Australia had all the ingredients to make optical glass, we did not have the procedures in place to do so. Optical glass is hard to form and expensive to produce; extraordinarily high temperatures are required to melt the quartz sands and these temperature make the mixture highly reactive. This can lead to contamination of the mixture through chemical reactions with containers that hold the molten glass. Optical glass is also a very viscous product, and it is difficult to get tiny bubbles out of the mixture. To make optical glass, fine sand and various mixtures of oxides, such as potash (potassium oxide), soda (sodium oxide), lime (calcium oxide) and magnesium oxide are melted together in a pot. The pot, or refractory, is lined with, or made of, special clays. As mentioned above, the glass produced in the refractory can be affected by impurities in the clay which leak out of the clay and into the 'melt' of optical glass. Australian Consolidated Industries, in conjuction with Professor Hartung from the University of Melbourne, tested over 100 clays from all over Australia until they found the right clays to use in their pot construction. In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

In June 1941, Hartung reported: Much work has been done on the testing and selection of suitable pot clays for melting optical glass. After the accumulation of sufficient evidence from our experiments in Melbourne, I went to Sydney towards the end of February last, and discussed the whole matter fully with the staff of Messrs. A.C.I. who are concerned with the development of the project. As a result, a standard blend of four pot clays was selected for use in the making of full scale pots for the production of optical glass.(2) Following the production of the 'melt', the optical glass is then poured into moulds which form prisms, lens blanks and slabs. Prism cubes of up to 5 inches (12.7 cm) and lenses of up to 8 inches (20.3 cm) were made by an Australian Consolidated Industries subsidiary: Australian Window Glass Pty Ltd, in Sydney. After moulding, the glass blanks are annealed. Annealing is the process of controlled thermal treatment to lower the level of strain inside the glass caused by uneven cooling. It involves raising the glass to a high enough temperature to relieve the strain, then the glass is gradually cooled again. Optical glass needs the most careful annealing because of the significant effect of residual strain on the final optical properties of the glass. (1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

(1) D.P. Mellor (1958), 'Optical Munitions', Australia in the War of 1939-1945: The Role of Science and Industry, ch. 12, series 4: civil, vol. 5, Australian War Memorial, Canberra, p. 255. (2) J.S. Rogers, The History of the Optical Munitions Panel: July 1940 - December 1946, Australian Archives, Brighton, Melbourne, MP 730/11, Box 3, p. 49. Published by the Australian Science Archives Project on ASAPWeb, 30 April 1997 Comments or corrections to: Bright Sparcs (bsparcs@asap.unimelb.edu.au) Prepared by: Denise Sutherland and Elissa Tenkate Updated by: Elissa Tenkate Date modified: 19 February 1998 | Top | Bright Sparcs | ASAPWeb |

High Power Objective (40x): This objective (sometimes called the "high-dry" objective) is useful for observing fine detail such as the striations in skeletal muscle, the arrangement of Haversian systems in compact bone, types of nerve cells in the retina, etc.