According to the NYT article: <a href="http:&#x2F;&#x2F;www.nytimes.com&#x2F;2015&#x2F;12&#x2F;03&#x2F;science&#x2F;q-carbon-harder-than-diamond.html" rel="nofollow">http:&#x2F;&#x2F;www.nytimes.com&#x2F;2015&#x2F;12&#x2F;03&#x2F;science&#x2F;q-carbon-harder-th...</a> The substence is &quot;magnetic, fluorescent and electroconductive&quot; so likely it&#x27;s referring to the fluorescent property and it had an electric current running through it during the demo.