Turning copper into a black body emissive radiator?

Curious…
Can a permanent ink felt marker (marks-a-lot, sharpie…etc) be used to color copper and make it an effective black body radiator?
thanks in advance

How many K do you want it to radiate at? Past a certain point...black won't matter

Seriously though, assuming this is lighting related, and we are talking LED heat sink temperatures, I think you would have more success with one of the matte black chrome platings used in the solar industry on thermal solar collectors. I'm not sure what the thermal transfer across the dye/copper interface would be, but I do remember from college that surface finish matters on a radiator, and rough was better than shiny. Perhaps a bead blasted surface dyed black with sharpie would work? But heat may degrade the dye over time.

many kinds of paint will work; remember it doesn't have to be black in the visible light range; it has to get rid of heat, infrared:
http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
http://snap.fnal.gov/crshield/crs-mech/emissivity-eoi.html

I have kitchen under cabinet LED lights on aluminum trim channel. I used 2 coats of a Sanford Sharpie to make a 1" diameter circle of black, and let it dry. Also painted one portion with high-temperature black spray paint, made to paint a gas grill.

2 Luxeon Rebels running at 900ma heat up this 14" long aluminum piece. After an hour, it is very warm.

With my trust IR temperature meter, the bare shiney aluminum reads 78 degrees (ya, right). The circle of Sharpie reads 86 degrees (F.) But the painted black area reads 105 degrees!

So the sharpie does not do a very good job at making a black body radiator. But spray paint does. Very interesting!

Jeff O.

jeffosborne said:

I have kitchen under cabinet LED lights on aluminum trim channel. I used 2 coats of a Sanford Sharpie to make a 1" diameter circle of black, and let it dry. Also painted one portion with high-temperature black spray paint, made to paint a gas grill.

2 Luxeon Rebels running at 900ma heat up this 14" long aluminum piece. After an hour, it is very warm.

With my trust IR temperature meter, the bare shiney aluminum reads 78 degrees (ya, right). The circle of Sharpie reads 86 degrees (F.) But the painted black area reads 105 degrees!

So the sharpie does not do a very good job at making a black body radiator. But spray paint does. Very interesting!

Jeff O.

Click to expand...

I suspect that this is due to the varying emissivities affecting your IR thermometer readings. I HIGHLY doubt that you are generating enough heat to make a foot-long aluminum bar vary by 27 degrees (15C). Blocks of Aluminum are 250 W/m*k thermal conductivity. If you've got 1/100th that, you'd need 70W. Read up on how the IR thermometer is affected by surfaces. You need special calibration (And surface selection!) to compare painted metal to shiny metal.

If you use the IR thermometer to measure the temp of the shiny side of two pieces of aluminium subject to the same heat load (but with your different surface treatments on the other side) you might get a more accurate relative answer, as emissivity won't interfere with the measurement. Or measure the temp near the LEDs with a different device (eg thermistor, thermocouple)... just an idea....

AnAppleSnail said:

I suspect that this is due to the varying emissivities affecting your IR thermometer readings. I HIGHLY doubt that you are generating enough heat to make a foot-long aluminum bar vary by 27 degrees (15C). Blocks of Aluminum are 250 W/m*k thermal conductivity. If you've got 1/100th that, you'd need 70W. Read up on how the IR thermometer is affected by surfaces. You need special calibration (And surface selection!) to compare painted metal to shiny metal.

Click to expand...

Yes, it is a common problem in pyrometry. I actually sell a high end "emissivity corrected pyrometer" sensor, and the effect is very large. (on the measurement, much less on the actual temperature).

Less obvious, is that the emissivity needs to be measured at the same wavelength as the pyrometer measurement or the results will still be substantially off, and it gets even more picky from there. It is even possible to have two paints that both look the same color to your eyes give completely different results from this effect.

These units are BMW sort of prices though, so definitely not for the consumer market.

If you are interested in making a black body radiator from copper, the most important thing is not the color, but the consistency of the surface. Consider rough sanding it, and then force oxidize it to a consistent look. (similar to anodizing aluminum) There are some artist techniques for copper that give that ugly green look - that is what you want.

"patina" is the search you want.
The problem is most if not all patinas will wear off on your hands!

Nevertheless, for those interested, for example here are some recipes: http://www.sciencecompany.com/-W160.aspx
NOTE, those are collected, not tested, and some involve stuff you really don't want to be careless with.
Kids, don't try this at home. Everyone, don't lick your fingers or inhale while using some of these chemicals.