We sometimes have people contact us gasping at the price difference between nickel and carbon paint. Some ask for comparisons between the two to understand the price difference. I've written this email too many times to count. I should have written this blog post a long time ago.
On the surface, you may think you're comparing similar products. I mean, they're both shielding paint, right? Well, not exactly... There are many key differences worth considering.
1) Number of Coats
Nickel paint generally only requires one thin/even coat per guitar, so you get way more out of it than you think. Depending on the size of the cavities, you could do a few guitars with single 12mL bottle of nickel paint. In contrast, good carbon paint requires at least 3 coats to be minimally effective. Most of the cheaper carbon shielding paint you find on the market requires 5+ coats.
2) Curing Time
With forced air assistance, nickel paint is fully cured in as little as 30 minutes. So, you could have a guitar painted, dried, and reassembled in less than an hour. Compare that to carbon paint, which takes hours to dry between coats (up to 12 hours for the "cheap" stuff). Meaning, using carbon shielding paint on a guitar can be a multi-day process by the time you're able to play it again. Carbon shielding paint may be much cheaper by the mL, but it is also much more time consuming to work with.
Not only is nickel shielding paint much more efficient, saving you a ton of time, but it is also significantly more effective. Nickel shielding paint not only provides superior protection against electromagnetic interference, but it also protects against magnetic fields, which carbon shielding paint does not.
In case you're into the technical side of things, shielding needs to have full continuity between all possible points for it to be properly effective. Continuity is defined as having 0 (or as close to 0 as possible) ohms resistance. Most meters that measure continuity allow for up to 50 ohms resistance before it stops beeping, which is actually quite high but that's beside the point. With nickel paint, you'll have less than 5 ohms resistance across the board with just one thin/evenly applied coat of paint (technique dependent, of course).
In contrast, you'll need at least 2 coats of good carbon paint (3-4 of cheap/budget carbon paint) to get intermittent continuity across all points. That means you'll have continuity when the probes are closer together, but no continuity between distant points. That's because the surface resistance of carbon is so much higher than nickel. Only after 3-4 coats of carbon paint (5-6 of the cheap stuff) will you have it consistently below 50 ohms across all points/distances on the instrument.
Still, no matter how many coats of carbon paint you apply, you will never get the resistance as low as just a single coat of the nickel paint. This is not salesmanship. These are very real, very measurable technical performance characteristics.
Frankly, they are different products meant for different people. If you are not concerned with time-sensitivity and minimal performance is enough, carbon paint is fantastic. It does a "good enough" job for most people. If you operate in a time-sensitive nature and prefer top quality performance, nickel paint would be the better choice.
For those reasons, nickel paint is the preferred product of most professional techs. It saves a ton of time (which means money), and does a better job.