Doofus, et al: The numbering system for heroin was developed by the US DEA. Here is the system:
#1: Morphine Freebase or Morphine HCl.
#2: Heroin Freebase.
#3: Heroin specifically prepared for smoking at the POM (point of manufacture). The technical requirement is a 60:40 mix with 60 representing the amount of heroin (as Mr. Blond correctly noted).
#4: Heroin specifically prepared for injection, i.e. any salt other than the Acetate, but almost always Hcl.
A couple of notes...The reason why #1 is morphine and not heroin per se is because at the time that this system was devised, in the very early 1970s, morphine and morphine freebase were specific illcit commodities themselves, and used in the production of heroin.
Unlike now, most heroin was made from morphine bought from illicit producers rather than the illicit manufacturers of heroin extracting morphine from opium themselves as an intermediate step in the production of heroin. Today there is only one tiny area of the world where morphine/morphine freebase remains a commodity in and of itself. While morphine freebase is still manufactured for sale in Wa Country in Mynammar (Burma), it is now only sold to Malaysian operators who manufacture #3, in the jungles on the Thai/Malaysian border country.
Indeed, this is the only place in the world where you can still see actual #3. Even in its traditional stronghold and place of invention, Hong Kong it is not gone forever. Aside from the 60:40 mix it also almost always has quinine and strychnine for flavour, and barbitone for potentiation. They no longer use colouring but at one time you could see purple, grey, bright red, and a pearl sheen which were used as a marketing ploy/trademark.
When the numbering system was devised "Tar Heroin" had not been invented. Technically it qualifies as #4 because it is made for injection, although the main objective is to turn a buck and not any kind of ultimate design for consumption.
Tar is NOT acetylated opium as many think. It is made via the use of a poor GAA (meaning other than AA also known as Acetic Anhydride) and a much different temp and time for the "cook" (acetylysation) which is performed without a Reflux Apparattus, which in turn selectively acetylses the opium given it a very high percentage of the MAMs (3 and 6) so that it is truly deserving of a revision in the classification system, but I am sure we will never see that.
Since this is "Aussie and Asia" I am sure we have some people who are familiar with yet another type of heroin, "Homebaked Heroin" which is basically "Tar" except that it is usually made from codeine instead of morphine.
Using O-demetylation they convert the codeine into morphine (or rather revert it since commercial codeine is usually made from morphine), then itis heated usually using AA (unlike "Tar"), but like "Tar" without Reflux. This is what is responsible for the black and gummy consistency.
One final note on the types, "Homebaked" USED to also come in a pink tar form when Diconal was used for the precursor but since Diconal has gone the way of the Dodo it is always black today...although "Homebaked" also seems to be going the way of the Dodo due to the increased availability of pepared heroin in Oz and NZ.
A note on the potentiation of heroin for smoking: #4 as has already been discussed, needs to have its MP (Melting Point) and VP (Vapourisation Point) brought into alignment, or you waste much of the heroin. By the time it melts, it has vapourised long before so that there is little if any active substance to metabolise.
Caffeine is the potentiator used by commercial manufactuers of #3, but any substance , inert or otherwise, that offers a lower MP will help in this quest. You can use the MP of caffeine hcl. as a guideline for which substance to use, and adjust porportions based on the 40% caffeine hcl. requirement. If it has a lower MP, you can use less of the potentiator, if has a higher MP you need to use more and so on.
Per the form used by the OP, that was smoked in the past, it was probably #2, heroin freebase since #3 is exceedingly rare, now only found in 2 Malaysian cities although it is not inconceivable that it would have made its way to Australia given its proximity to Malaysia, etc.
#2 can be smoked without any alteration whatsoever because of freebase's natural MP. It can also be insufflated without any alteration because the nasal mucous salinity naturally adjusts the pH. Injection though requires an acidic catalyst. Usually citirc acid is used.
As for where to locate caffeine hcl., I feel it does not skirt the "No Sourcing" rule to state that one can find Rx pure caffeine hcl in bulk form in many health food stores as well as in Wholesale Pharmacies and the like. Oz has stringent controls so I would imagine one would have to limit one's self to a personal use amount (which is what I imagine the OP is discussing in any event), and locate it domesetically to avoid running afoul of regulations or even laws.
Good luck.
