AFOAF has plenty of first hand experience. AFOAF is also a chemist, and has performed several extractions (using legitimate lab equipment like Bucchi rotavaps, and HPLC grade non-stabilized 99.996% ether)
from reading Microgram bulletin, other journals/references, first hand experience...
AFOAF can be quite certain that the following is accurate:
1) "brown tar" or "brown powder" is generally a relatively high OPIATE purity "no 2" (free base) heroin.
it is not high purity HEROIN (eg: diacetyl morphine), but instead high purity OPIATE.
uncut material (which AFOAF has received on many occasions, visibly cut from kilogram blocks in 25 gram "balls") is likely upwards of 80% OPIATE (at the very least).
what does this mean? It means that the central/south american groups that process this material do not have the faculties and experience to produce high purity DIAMORPHINE in high yield.
instead, the product is a mixture of morphine, both mono-acetyl intermediates, and diamorphine (heroin), as well as impurities like codeine, excess acetic acid, and water.
the production method does not include a dehydration step (in the laboratory, you would use a dehydrating agent like Na2SO4 and a Brine wash), and thus the product sold is the HYDRATE.
this mixture results in innaccurate claims that mexican brown powder is "low quality" or "low potency"
it just simply has a lower proportion of the actual heroin to the other reaction intermediates and starting material as opposed to central/southeast asian heroin.
2) brown powder, and indeed most "domestic" forms of heroin are rarely cut, because most are found originally as a freebase.
cutting a freebase is extremely difficult (in comparison to central/southeast asian no 4 HCl and sulfate salts).
the freebase is often sticky/oxidized (though not tar like, that I will come to in a moment), and does not easily "mix" with a cutting agent.
when it is cut, it is usually done so before it is packaged in balloons (because the only groups/gangs with the resources to cut this material successfully/economically are the same groups that sell it on the streets)
again: AFOAF's experience is that Balloons are usually cut, whereas large chunks of the raw, unpackaged material are usually NOT cut.
3) Brown powder is not "new." it is simply the fact that Mexican gangs have relatively recently stepped up their efforts. A quick Google News search will corroborate the claim that there has been a relatively recent significant increase in the influx of central/south american heroin across the US border.
so basically, it is not new, it is just more commonly available than it used to be, and so it is proportionately more common than Tar.
it is also way cheaper than it was 10 years ago. 10 years ago, balloons were pretty much the only easy way to get it, and they would run NO PRICES in LA barrios...
now, you can routinely buy the stuff as gram chunks for NO PRICES (which works out to about NO PRICES per balloon, according to the usually weight of 0.20 to 0.25 grams per balloon)
AFOAF used to get "balls" (Ball = 25 grams, not an "8 ball" which is different) of extremely fresh (AFOAF used to call it "fresh off the brick"), powdery, extremely pungent material for NO PRICES .
AFOAF is white, and was, by no means, getting a good deal. Hispanic associates of AFOAF who were dealing with the same individuals routinely purchased the same quantities for NO PRICES /25 gram ball.
4) Tar. AFOAF's experience with Tar seems to indicate that Tar is actually produced in a completely different method.
Whether Tar comes over the border that way, or is converted Domestically is an open question...
however, it is evident from AFOAF's experience that the SIGNATURE characteristic of Brown powder (the existence of non-heroin morphine alkaloids) ARE NOT PRESENT in the Tar....
AFOAF bases this on a few pieces of anectdotal and direct evidence:
discussions of purity have taken place in publications, claiming that Brown powder has 5-10% heroin, whereas tar may have as much as 20% heroin... YET we all know that Tar is less potent.
AFOAF actually extracted both using the proper tools and materials, and the Tar produces significantly more product than the powder (10% yield of brilliant white, extremely potent powder from Tar, vs a thick, sticky orange paste from the powder)
this would suggest that the composition of the 2 materials is significantly different.
this would further suggest that Tar is NOT a simple "highly cut" version of the brown powder, and is most likely a completely different beast altogether.