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<p>[QUOTE=&quot;GoldFinger1969, post: 26090047, member: 73489&quot;]Wow, I did NOT know that. <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie100" alt=":wideyed:" unselectable="on" unselectable="on" /></p><p><br /></p><p>I suspect that others will chime in here -- pro and/or con -- and I will not have to ask any questions on that.</p><p>The best explanation of luster I have read -- at least for Double Eagle gold coins -- comes from Roger Burdette&#039;s <b><i>magnus opus </i></b>on Saint-Gaudens DEs:</p><p><br /></p><p><i>Luster, as understood by coin collectors, <b><span style="color: #0000ff">is the visual result of light reflecting off of thousands of tiny ridges and grooves of metal in the smooth (i.e., field) areas of a coin. These imperfections were created in a working die as the hard steel was stressed during the striking of thousands of blank planchets.</span></b></i></p><p><i><b><span style="color: #0000ff"><br /></span></b></i></p><p><i>The original surface of a coinage die is smooth, somewhat satin-like and largely free of imperfections. This die face is made of very hard carbon steel (mostly martensitic steel formed by rapid cooling of austenite steel) that has been tempered for toughness. Modern techniques further harden the surface through application of special coatings, but this was not done on dies made for Saint-Gaudens double eagles.</i></p><p><i><br /></i></p><p><i>In use, the hard die face impacted a soft metal planchet composed of 0.900 gold and 0.100 copper. The pressure, or force, applied to the planchet was approximately 100 tons to 120 tons per square inch acting over a short period of time. Energy of the blow, pushed planchet metal into the recesses of the die so that the coin became a mirror image of the die face. <b><span style="color: #0000ff">With each blow of the die, an imperceptible movement occurred in the crystals of the die face. Following several hundred strikes, the die face had distorted slightly so that the fields were no longer com-pletely smooth, but consisted of microscopic ridges and grooves.</span></b> These radiaated from the center of the die face and also emulated the general pattern of metal flow in the planchets. Once metal flow was established, it tended to aid metal flow in planchets and the die surface then changed very slowly.</i></p><p><i><br /></i></p><p><i>This type of surface alteration was most prominent in the fields of a die where movement of metal was greatest and least inhibited by details of the design. The portrait, inscriptions and other design elements were subject to similar die deformation, but at a much lower rate and magnitude. <b><span style="color: #0000ff">This explains why a coin shows luster in the fields but not in the raised areas.</span></b></i></p><p><i><br /></i></p><p><i>If a die is kept in use too long, or was improperly tempered, surface distortion will con-tinue to where ridges and groves appear to join into larger structures. Their amplitude also in-creases and the defects become visible streaks on the die surface. This also begins to abrade the edges of details and creates additional ridges that blur design detail. At this point, the die is said to exhibit “starburst” named for the bright star-like pattern of radial lines.</i></p><p>I know Mark is an ex-grader and has helped me on other forums.&nbsp; I did not know he had written about luster and/or the physics of luster.&nbsp; If you can direct me to what he wrote or where he wrote it, I would be most appreciative.</p><p>No doubt that luster on a large gold Double Eagle is going to look different than the luster on a much smaller dime or nickel comprised of different metals.&nbsp; That&#039;s an excellent point.[/QUOTE]</p><p><br /></p>

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