Does purple on copper mean "acetone"?
zeebob
Posts: 2,825 ✭
Last Friday, a dealer was looking at a large cent that I own. The cent (1838) is in an NGC holder marked MS65BN. The dealer seemed to like the coin a lot. For the sake of full disclosure, I mentioned that I tried to cross the coin into PCGS plastic, but PCGS declined because of questionable color (there is just a hint of purple on the reverse in a couple of areas).
The dealer immediately lost interest. He said that purple meant someone had used acetone on the coin and failed to rinse it.
Is that what purple means?
The dealer immediately lost interest. He said that purple meant someone had used acetone on the coin and failed to rinse it.
Is that what purple means?
0
Comments
I can't imagine acetone turning copper purple.
"Inspiration exists, but it has to find you working" Pablo Picasso
The Penny Lady®
However a blue or purple sheen can mean MS-70.
Collector of Early 20th Century U.S. Coinage.
ANA Member R-3147111
http://www.sunysb.edu/vescalab/research/research7.html
Photochemical Breakdown of Acetone on Copper
Sanjay V. Kagwade, Clive R. Clayton, Devicharan Chidambaram and
Gary P. Halada
Electrochemica Acta 46, 15 (2001) 2337-2342.
X-ray Photoelectron Spectroscopy studies have shown that acetone, when used as a cleaning agent for copper in the presence of ambient light and water vapor, slowly reacts to form acetic acid. This reaction does not occur in the absence of light. This suggests that copper acts as a photocatalyst for the reaction between acetone and water vapor. The use of acetone for degreasing copper and copper containing alloys as recommended by ASTM E1078-97 is questioned in this work.
Copper reacts photochemically with acetone and water vapor to form acetic acid. The acetic acid then reacts with copper to form copper acetate. Over a period of 18 hours the copper foil that was immersed in acetone and exposed to ambient light developed blue crystal deposits as shown in the optical photomicrograph in Fig. 1(left). The acetone in the beaker had evaporated leaving behind a strong odor of acetic acid. In contrast, there were no visible changes observed on the copper foil that was exposed to acetone in darkness as shown in Fig. 1(right). The acetone in the beaker in this case had evaporated, leaving behind no distinguishable odor of any byproduct. The decomposition of acetone appears to be completely inhibited in darkness. The following reaction sequence was proposed:
CH3COCH3 + H2O CH3COOH + CH4
2(CH3COOH) + Cu Cu(COOCH3)2 + H2
CH3COOH (aq.) + e- CH3COO- (aq.) + 1/2 H2
Cu(CH3COO)2 + Cu(0) 2 Cu(CH3COO)
Acetone should not be recommended for degreasing or cleaning of copper or copper bearing alloys containing discrete copper rich intermetallic particles. Though ASTM E1078-97 "Standard Guide for Specimen Preparation and Mounting in Surface Analysis" recommends that prior to surface analysis samples should be ultrasonically degreased in analytical grade acetone and isopropanol, based on this work acetone is not recommended to be used for degreasing copper or copper containing alloys. Also one of the other studies performed in this lab has shown that isopropanol has no such effects on copper, and hence we recommend the use of isopropanol alone for degreasing.
References:
S.V. Kagwade, C.R. Clayton, in P.M. Natishan, H.S. Isaacs, M. Janik-Czachor, V.A. Macagno, P. Marcus, M. Seo (Editors), Passivity and Its Breakdown, The Electrochemical Society, Pennington NJ, 1997, p. 631.
S.V. Kagwade, C.R. Clayton, D. Chidambaram, M.L. Du, F.P. Chiang, Journal of the Electrochemical Society 147 (2000) 4125.
D. Chidambaram, G.P. Halada, Surf. Inter. Anal. 31 (2001) 1056.
(a) 0.25 cm (b)
Fig. 1. Optical photomicrographs of copper foils exposed to acetone for 18 hours in either (a) ambient light or (b) darkness.
isopropanol!
<< <i>Last Friday, a dealer was looking at a large cent that I own. The cent (1838) is in an NGC holder marked MS65BN. The dealer seemed to like the coin a lot. For the sake of full disclosure, I mentioned that I tried to cross the coin into PCGS plastic, but PCGS declined because of questionable color (there is just a hint of purple on the reverse in a couple of areas).
The dealer immediately lost interest. He said that purple meant someone had used acetone on the coin and failed to rinse it.
Is that what purple means? >>
At least you know what not to say and what to do the next time someone is marvelling over your coin.
Leo
The more qualities observed in a coin, the more desirable that coin becomes!
My Jefferson Nickel Collection
<< <i>At least you know what not to say and what to do the next time someone is marvelling over your coin. >>
Go figure.
What was he trying to do by being honest?
"Inspiration exists, but it has to find you working" Pablo Picasso
<< <i>
<< <i>Last Friday, a dealer was looking at a large cent that I own. The cent (1838) is in an NGC holder marked MS65BN. The dealer seemed to like the coin a lot. For the sake of full disclosure, I mentioned that I tried to cross the coin into PCGS plastic, but PCGS declined because of questionable color (there is just a hint of purple on the reverse in a couple of areas).
The dealer immediately lost interest. He said that purple meant someone had used acetone on the coin and failed to rinse it.
Is that what purple means? >>
At least you know what not to say and what to do the next time someone is marvelling over your coin.
Leo >>
I sleep better at night by following "full disclosure." I'll continue to do so.
<< <i>I doubt that it caused purple bust I found this study that I found very interesting...
http://www.sunysb.edu/vescalab/research/research7.html
Photochemical Breakdown of Acetone on Copper
Sanjay V. Kagwade, Clive R. Clayton, Devicharan Chidambaram and
Gary P. Halada
Electrochemica Acta 46, 15 (2001) 2337-2342.
X-ray Photoelectron Spectroscopy studies have shown that acetone, when used as a cleaning agent for copper in the presence of ambient light and water vapor, slowly reacts to form acetic acid. This reaction does not occur in the absence of light. This suggests that copper acts as a photocatalyst for the reaction between acetone and water vapor. The use of acetone for degreasing copper and copper containing alloys as recommended by ASTM E1078-97 is questioned in this work.
Copper reacts photochemically with acetone and water vapor to form acetic acid. The acetic acid then reacts with copper to form copper acetate. Over a period of 18 hours the copper foil that was immersed in acetone and exposed to ambient light developed blue crystal deposits as shown in the optical photomicrograph in Fig. 1(left). The acetone in the beaker had evaporated leaving behind a strong odor of acetic acid. In contrast, there were no visible changes observed on the copper foil that was exposed to acetone in darkness as shown in Fig. 1(right). The acetone in the beaker in this case had evaporated, leaving behind no distinguishable odor of any byproduct. The decomposition of acetone appears to be completely inhibited in darkness. The following reaction sequence was proposed:
CH3COCH3 + H2O CH3COOH + CH4
2(CH3COOH) + Cu Cu(COOCH3)2 + H2
CH3COOH (aq.) + e- CH3COO- (aq.) + 1/2 H2
Cu(CH3COO)2 + Cu(0) 2 Cu(CH3COO)
Acetone should not be recommended for degreasing or cleaning of copper or copper bearing alloys containing discrete copper rich intermetallic particles. Though ASTM E1078-97 "Standard Guide for Specimen Preparation and Mounting in Surface Analysis" recommends that prior to surface analysis samples should be ultrasonically degreased in analytical grade acetone and isopropanol, based on this work acetone is not recommended to be used for degreasing copper or copper containing alloys. Also one of the other studies performed in this lab has shown that isopropanol has no such effects on copper, and hence we recommend the use of isopropanol alone for degreasing.
References:
S.V. Kagwade, C.R. Clayton, in P.M. Natishan, H.S. Isaacs, M. Janik-Czachor, V.A. Macagno, P. Marcus, M. Seo (Editors), Passivity and Its Breakdown, The Electrochemical Society, Pennington NJ, 1997, p. 631.
S.V. Kagwade, C.R. Clayton, D. Chidambaram, M.L. Du, F.P. Chiang, Journal of the Electrochemical Society 147 (2000) 4125.
D. Chidambaram, G.P. Halada, Surf. Inter. Anal. 31 (2001) 1056.
(a) 0.25 cm (b)
Fig. 1. Optical photomicrographs of copper foils exposed to acetone for 18 hours in either (a) ambient light or (b) darkness. >>
This isn't really relevant to the discussion since it involves the reaction of a common acid found in vinegar with copper to give blue divalent copper salts. OTOH the cuprous or copper (I) form does indeed form purple colored complexes with spectrophotometric reagents such as the biquinolines. There have been comments here in the past about copper coins developing purple discoloration when exposed to acetone. This would be possible if the acetone was contaminated somewhere along the supply chain. If feasible ALWAYS use acetone that was known to be distilled in glass and packaged in glass when using it on coins.
<< <i>I also concur with MS70 being the likely cause. >>