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<p>[QUOTE="GSDykes, post: 4023629, member: 73321"]A partial quote from classicalcoins.com:</p><p><br /></p><p><b>Conservation Measures </b></p><p><br /></p><p>Time: An Essential Ingredient </p><p><br /></p><p>The chlorides causing bronze disease pervaded the specimen over hundreds or thousands of years, and they won’t leave instantly. Treating bronze disease is a time-consuming process – no quick "solution" will leave the specimen relatively intact. Electrolysis (like other “quick fixes) inevitably leads to recurrence of corrosion and ultimate disaster. To do the job right and prevent recurrence, one must be vigilant, knowledgeable and patient - in some cases, it may take a year or more to stabilize the specimen.</p><p><br /></p><p>Dessication</p><p><br /></p><p>The least invasive countermeasure to halt progression of bronze disease is dessication - removing water needed to sustain the corrosion reaction. Baking at 250 degrees for at least 30 minutes does that. Once the specimen cools, water vapor in the air may be absorbed and act to restart the reaction. If the specimen is instead placed in an airtight container with a moisture absorbent such as silica gel, it will be safe until further conservation can begin. </p><p><br /></p><p>It has been reported that such heating may tend to darken a coin’s patina. Thus, it is best not to exceed 250o F during dessication.</p><p><br /></p><p>Treating Incipient Cases</p><p><br /></p><p>In cases where bronze disease is beginning to appear, soaking the specimen in distilled water (NOT chlorine-containing tap water) may suffice. Since moisture is needed to start the reaction, soaking in water may seem counter-intuitive. However, distilled water attracts chloride ions resident on or within a coin into solution, gradually removing them from the coin. As the water becomes saturated with chloride ions its effectiveness in removing chlorides diminishes, so changing the water periodically is necessary. The water should be changed every few days at first, and then weekly. Periodically check progress by drying the coin and examining it. Repeat the soaking as needed. In many cases, this is all that will be required to stabilize the specimen.</p><p><br /></p><p>Treating More Advanced Cases</p><p><br /></p><p>Sodium Sesquicarbonate Immersion </p><p><br /></p><p>1) Open up every pore site where bronze disease is progressing with a toothpick or (very carefully) with a steel needle, so that the solution can penetrate to the corrosion sites. It is permissible to remove corrosion products for appearance reasons, although that does not additionally contribute to halting bronze disease. Dessicate the specimen.</p><p><br /></p><p>2) During dessication, if made-up solution is not already on hand, prepare a 2% (by weight) aqueous solution of sodium sesquicarbonate in distilled water. If one doesn't have easy access to sodium sesquicarbonate, it can be made up from equal molar quantities of sodium carbonate (or soda ash - Na2CO3) and sodium bicarbonate (NaHCO3). A 2% solution would dissolve 4.24 g of sodium carbonate and 3.36 g of sodium bicarbonate in 100 ml of distilled water. </p><p><br /></p><p>Although many conservation authorities recommend a 5% sesquicarbonate solution, this strength will strip the patina from a specimen. The weaker 2% solution takes three times as long (and may be ineffective), but the reaction is slowed enough to allow monitoring and ending the soak before the patina is stripped. Use a 5% solution only if the 2% solution fails to stabilize, and if the conservator is prepared to accept a stripped specimen. Otherwise, repeat the distilled water soak and 2% sesquicarbonate solution immersion as many times as is required to stabilize the specimen.</p><p><br /></p><p>3) Place the specimen in a covered glass container (a Petri dish is suitable, as is the 8 oz. “jelly jar” used by home canners), and fill with a 2% solution of sodium sesquicarbonate until the specimen is well covered. Soak for two weeks, replace the solution, then soak the specimen for another two weeks or until a greenish color begins to appear in the solution - indicating that the patina is beginning to dissolve. Rinse the coin thoroughly in tap water. </p><p><br /></p><p>4) Soak the specimen in distilled water for 24 hours. Dry, then perform a silver nitrate test per<a href="http://www.nps.gov/museum/publications/conserveogram/06-03.pdf" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.nps.gov/museum/publications/conserveogram/06-03.pdf" rel="nofollow"> Testing For Chlorides With Silver Nitrate</a> . Use this procedure: “To Test for Chlorides in Objects Not Yet in Treatment.” </p><p><br /></p><p>5) If necessary, repeat steps 3) and 4) until the silver nitrate test is negative. Dry the specimen thoroughly. Do NOT seal its surface with lacquer or wax. </p><p><br /></p><p>Chlorine ions have now been removed from its surface. If the specimen is kept in a dry environment, bronze disease should not recur. </p><p><br /></p><p>Treating Serious Cases </p><p><br /></p><p><b> Additional steps for preventing recurrence of bronze disease</b> normally are only necessary for objects that cannot be kept in a dry environment, or are internally pervaded by chloride ions. Do not attempt such treatment unless safety precautions for handling toxic materials are understood.</p><p><br /></p><p><i><b> IMPORTANT OBSERVATIONS</b></i></p><p><br /></p><p>Specimens subjected to conservation measures that improve their appearance (e.g. coins pitted by bronze disease) may not ethically be sold without full disclosure to the buyer. <b> Classical Coins will not acquire or sell any coin whose appearance has been improved by such measures.</b></p><p>end partial quote</p><p><br /></p><p>note the final warning!!</p><p>Gary in Washington[/QUOTE]</p><p><br /></p>
[QUOTE="GSDykes, post: 4023629, member: 73321"]A partial quote from classicalcoins.com: [B]Conservation Measures [/B] Time: An Essential Ingredient The chlorides causing bronze disease pervaded the specimen over hundreds or thousands of years, and they won’t leave instantly. Treating bronze disease is a time-consuming process – no quick "solution" will leave the specimen relatively intact. Electrolysis (like other “quick fixes) inevitably leads to recurrence of corrosion and ultimate disaster. To do the job right and prevent recurrence, one must be vigilant, knowledgeable and patient - in some cases, it may take a year or more to stabilize the specimen. Dessication The least invasive countermeasure to halt progression of bronze disease is dessication - removing water needed to sustain the corrosion reaction. Baking at 250 degrees for at least 30 minutes does that. Once the specimen cools, water vapor in the air may be absorbed and act to restart the reaction. If the specimen is instead placed in an airtight container with a moisture absorbent such as silica gel, it will be safe until further conservation can begin. It has been reported that such heating may tend to darken a coin’s patina. Thus, it is best not to exceed 250o F during dessication. Treating Incipient Cases In cases where bronze disease is beginning to appear, soaking the specimen in distilled water (NOT chlorine-containing tap water) may suffice. Since moisture is needed to start the reaction, soaking in water may seem counter-intuitive. However, distilled water attracts chloride ions resident on or within a coin into solution, gradually removing them from the coin. As the water becomes saturated with chloride ions its effectiveness in removing chlorides diminishes, so changing the water periodically is necessary. The water should be changed every few days at first, and then weekly. Periodically check progress by drying the coin and examining it. Repeat the soaking as needed. In many cases, this is all that will be required to stabilize the specimen. Treating More Advanced Cases Sodium Sesquicarbonate Immersion 1) Open up every pore site where bronze disease is progressing with a toothpick or (very carefully) with a steel needle, so that the solution can penetrate to the corrosion sites. It is permissible to remove corrosion products for appearance reasons, although that does not additionally contribute to halting bronze disease. Dessicate the specimen. 2) During dessication, if made-up solution is not already on hand, prepare a 2% (by weight) aqueous solution of sodium sesquicarbonate in distilled water. If one doesn't have easy access to sodium sesquicarbonate, it can be made up from equal molar quantities of sodium carbonate (or soda ash - Na2CO3) and sodium bicarbonate (NaHCO3). A 2% solution would dissolve 4.24 g of sodium carbonate and 3.36 g of sodium bicarbonate in 100 ml of distilled water. Although many conservation authorities recommend a 5% sesquicarbonate solution, this strength will strip the patina from a specimen. The weaker 2% solution takes three times as long (and may be ineffective), but the reaction is slowed enough to allow monitoring and ending the soak before the patina is stripped. Use a 5% solution only if the 2% solution fails to stabilize, and if the conservator is prepared to accept a stripped specimen. Otherwise, repeat the distilled water soak and 2% sesquicarbonate solution immersion as many times as is required to stabilize the specimen. 3) Place the specimen in a covered glass container (a Petri dish is suitable, as is the 8 oz. “jelly jar” used by home canners), and fill with a 2% solution of sodium sesquicarbonate until the specimen is well covered. Soak for two weeks, replace the solution, then soak the specimen for another two weeks or until a greenish color begins to appear in the solution - indicating that the patina is beginning to dissolve. Rinse the coin thoroughly in tap water. 4) Soak the specimen in distilled water for 24 hours. Dry, then perform a silver nitrate test per[URL='http://www.nps.gov/museum/publications/conserveogram/06-03.pdf'] Testing For Chlorides With Silver Nitrate[/URL] . Use this procedure: “To Test for Chlorides in Objects Not Yet in Treatment.” 5) If necessary, repeat steps 3) and 4) until the silver nitrate test is negative. Dry the specimen thoroughly. Do NOT seal its surface with lacquer or wax. Chlorine ions have now been removed from its surface. If the specimen is kept in a dry environment, bronze disease should not recur. Treating Serious Cases [B] Additional steps for preventing recurrence of bronze disease[/B] normally are only necessary for objects that cannot be kept in a dry environment, or are internally pervaded by chloride ions. Do not attempt such treatment unless safety precautions for handling toxic materials are understood. [I][B] IMPORTANT OBSERVATIONS[/B][/I] Specimens subjected to conservation measures that improve their appearance (e.g. coins pitted by bronze disease) may not ethically be sold without full disclosure to the buyer. [B] Classical Coins will not acquire or sell any coin whose appearance has been improved by such measures.[/B] end partial quote [B][/B] note the final warning!! Gary in Washington[B][/B][/QUOTE]
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