Well, evidently things have changed.
Number 3 was often termed 'china white' but in truth was produced in SE Asia, mostly in the Shan States in Myanmar.
Samples were typically 90-95% pure diamorphine hydrochloride, the remainder being caffeine added to lower the melting-point thus making it smokable.
But as with all such things, it's another 'mystery powder game'.
The user cannot even PRESUME it cannot be more than 100% heroin so that half a point snorted will give someone without tolerance both a flash and a sustained nod.
The term 'china white' was depricated (at least in the USA) after George Marquardt began producing α-methyl fentanyl. I think the reasons he went with αMF were pragmatic. It was technically legal, it's duration of action was similar to heroin and with a potency some x60 diamorphine, it was highly profitable. It was only discovered after a cluster of apparent fatal ODs turned up but the coroners were unable to find the expected opioids.
I'm unsure if GM also understood the limits of analytical chemistry of the time but initially the DEA mis-identified αMF as 3MF, temporarily scheduled the wrong drug which meant he could carry on in spite of the fact that the DEA had figured out it was the work of a single 'cook' based in the USA itself.
Sidenote - The very same P2P used to synthesize is also used in the synthesis of αMF and although I don't understand US Federal law in detail, even IF caught with P2P, I suspect GM had worked out that claiming it was intended to be used in the production of αMF MAY have been a defence in law.
But truly - vape an absolutely tiny dot of the stuff off foil and wait for 10 minutes. H has a very distinctive taste and smell. One of those things like decaying flesh. Once you have smelt it you will NEVER forget as almost without exception, it means nothing good.
Using pins really does increase the risks and as I noted, unless things have changed, china white can be snorted or smoked and if done properly, both alternatives can achieve almost the same total bioavailability.
I just think injecting mystery powders is not 'a game for all the family' but I enclose a link to the above booklet. It's your body so all I will do is try to provide information so you can make a more informed choice.