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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
Posted to rec.crafts.metalworking
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Blackening Aluminum
Hi Jerome,
Can this finish be used in long-term exterior conditions? Does it rub off with use or is the color part of the aluminum? On Saturday, August 12, 1995 at 3:00:00 AM UTC-4, J. Kimberlin wrote: There have been several postings about blackening aluminum recently. I wrote an article for *Live Steam* magazine back about 1977 on the subject and have modified it a little since then. I do use it myself and thought that it would be of interest to the newsgroup. So: BLACKENING ALUMINUM by JEROME KIMBERLIN There are several ways to color aluminum black and among them are black anodizing and paint. You could rub dirt into the aluminum surface, I suppose, but of all the methods, I think chemical coloring is the superior method. It is certainly cheaper, faster, and home use allows the model engineer greater flexibility in the timing of his decoration of models in progress. Surface preparation of parts to be colored black is all important as any irregularities are not covered by this finish. Paint does build up and fill in scratches and other voids. Castings, however, should look like castings if the prototype used castings, so surface finish is always adjustable to the builders idea. The point here is to emphasize that this blackening technique will not cover up mistakes. You will need three chemicals. These a Nitric Acid , Copper Nitrate , and Potassium Permanganate . You will also need some good quality water - either distilled or deionized . I will give the dimensions of the mixture in both metric and English units so that both types of measures are accommodated: Take: water 3 quarts 750ml Add Acid 1/2 oz 5ml Add Copper 3 oz 25gm Add Permanganate 1 oz 10gm Add Water to make 1 gal 1 liter Obviously you will have to make up more or less solution to fill the container you will use to color aluminum parts and the parts to be colored should be completely covered by the solution. You should use a glass or plastic container. A metal container will poison the solution prematurely. At 75 degrees F (24 C) temperature, the blackening process will take about 15 minutes using a fresh solution. If it takes longer it means the solution is deficient in one of the compo nents. Usually, copper nitrate and nitric acid need be added. Aluminum is a strange metal to most of us. While we cannot see it, the surface of a newly machined or cleaned piece of aluminum combines with oxygen in the air to form a self protecting coating of aluminum oxide. This happens within minutes. If this surface continues to grow (get thicker) the blackening solution described here will not work satisfactorily. Thus, the piece to be colored should be cleaned just before immersing into the coloring solution. In my experience, glass bead blasting is a superior way to clean the aluminum surface and the choice of bead size determines surface finish. Once the bead blasting has been accomplished, the beads can be washed off with hot water and the aluminum piece immersed in the blackening solution. I recommend that the time between blasting (cleaning) and immersion in the blackening solution be less than two hours. I once waited five hours and was disappointed in the results. Once the blackening process has been completed, wash off the workpiece with tap water, drain and spray with WD-40 or other water displacing oil. There are a number of ways to clean aluminum satisfactorily. It is possible to simply sand the surface clean, or scrub it clean with an abrasive. One can also chem clean aluminum by degreasing the workpiece then dipping it into lye (Draino, for instance) for a few minutes or seconds as required, then rinsing. The shape of the workpiece and the model engineer's facilities often dictate what method of surface preparation will be used. Model engineers wishing to use this solution to blacken aluminum castings or other parts should be aware that the chemical components may be hazardous. While the solution itself is not particularly dangerous it can make your hands purple, so use rubber or plastic gloves. Potassium Permanganate is classified as an oxidizer even though dilute solutions of it are used throughout the world to sterilize vegetables used in salads, etc. Concen trated nitric acid is just plain bad. The technique for using it is to pour out a little in a glass container and then use an eye dropper to transfer the liquid to a measuring container when the volume wanted is small, such as that described here. Nitric acid also turns your hands yellow, hurts, and removes fingerprints. A good way to avoid eye damage is to wear a face shield such as the one you should be wearing when working in front of your grinder. I think I wrote this in Wordperfect 5.1 for DOS. I hope those interested do not have too much trouble interpreting... JerryK |
#2
Posted to rec.crafts.metalworking
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Blackening Aluminum
On Thursday, January 30, 2020 at 12:26:05 PM UTC-5, wrote:
Hi Jerome, Can this finish be used in long-term exterior conditions? Does it rub off with use or is the color part of the aluminum? You are replying to a 25 year old message. Do you really expect the person to reply? The chances are very slim that he's still even on Usenet. |
#3
Posted to rec.crafts.metalworking
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Blackening Aluminum
On 1/30/2020 5:17 PM, Michael Terrell wrote:
On Thursday, January 30, 2020 at 12:26:05 PM UTC-5, wrote: Hi Jerome, Can this finish be used in long-term exterior conditions? Does it rub off with use or is the color part of the aluminum? You are replying to a 25 year old message. Do you really expect the person to reply? The chances are very slim that he's still even on Usenet. I'm still on Usenet. LOL. |
#4
Posted to rec.crafts.metalworking
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Blackening Aluminum
On Saturday, February 1, 2020 at 2:10:03 PM UTC-5, Bob La Londe wrote:
On 1/30/2020 5:17 PM, Michael Terrell wrote: On Thursday, January 30, 2020 at 12:26:05 PM UTC-5, wrote: Hi Jerome, Can this finish be used in long-term exterior conditions? Does it rub off with use or is the color part of the aluminum? You are replying to a 25 year old message. Do you really expect the person to reply? The chances are very slim that he's still even on Usenet. I'm still on Usenet. LOL. So am I, but neither of us re the OP. Usenet is becoming a ghost town. |
#5
Posted to rec.crafts.metalworking
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Blackening Aluminum
usenet? Who uses this term in 2020?
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#6
Posted to rec.crafts.metalworking
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Blackening Aluminum
On 3/7/2020 7:28 PM, wrote:
usenet? Who uses this term in 2020? People who know what Usenet is. |
#7
Posted to rec.crafts.metalworking
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Blackening Aluminum
On Sat, 7 Mar 2020 18:28:02 -0800 (PST), wrote:
usenet? Who uses this term in 2020? The people who use Usenet. __ "Journalists are extremely rare and shouldn’t be harmed, but propagandists are everywhere and should be hunted for sport" Yeah..with no bag limit. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
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