In the US, basically all powder IS #4. I am sure someone must have already broken it down here but just to clarify:
There are 4 numbers utilised when describing heroin, 1 through 4.
Heroin #1 is merely morphine freebase.
Heroin #2 is heroin freebase.
Heroin #3 is heroin specifically manufactured, in SE Asia, for smoking.
Heroin #4 is heroin hcl specifically manufactured for injection.
Tar falls outside the numbering system, I will explain. In the very early 1970s, when the DEA was created, there was no Tar. Morphine freebase was given a number because of the (then) customary practice of using morphine freebase as a commodity to be bought and sold along the manufacturing pipeline.
For example, certain Turkish, Lebanese, Syrian and Golden Triangle manufactuers would handle nothing but morphine. It takes less chemicals and can be made oh so simply, and at the time high quality heroin producers did not want to be bothered with the entire synthesis.
Today it is rarely if ever produced and if it is found at all it will be in Burma for trade in Southern Thailand/Northern Malaysia.
#2, heroin freebase, is only made in the Golden Crescent, in Southern and Central Asia, primarily Afghanistan. This is the type perdominantly found in Europe as well as Indonesia (a curious twist that one). It is smoked as is, because the melting point and vapourisation point for heroin freebase are so closely synchronised. It is very rarely even heard of in North America.
Designed as an intermediate form in the manufacturing process, it became popular in Europe when South and Central Asian distributors took advantage of the European penchant for #3.
It can only be injected with an acidic catalyst to rectify the pH differential. Most people use some citric acid to convert it to an injectable form (an acid, though very rough one).
It can be insufflated (sniffed) with little difficulty because the salinity in your nasal mucous will convert its pH to almost optimum range.
#3 is heroin hcl, or rarely just heroin acetate. At the point of manufacture the "cook" adds caffeine to synchronise the melting and vapourisation points as well as flavorants (quinine, strychnine, etc) and sometimes colourants. Its colour can be red, purple, grey and so on. It is also usually produed in uniformly produced granules which look like pieces of rice.
This type has only ever ben produced in the Goldent Triangle and was only ever popular in Bangkok, Southern Thailand, Peninsular Malaysia and Hong Kong. It is now believed to be extinct, with the last labs (same ones actually using #1) in the northern jungles of Malaysia being taken down in 2004.
Its history is directly related to the Shanghai Heroin Pills produced in legal factories in the 1920s and 30s. Although not compounded as a tablet its ingredients are almost identical.
#4 was the first type of heroin ever produced, and remains the dominant form everywhere but Europe and Indonesia. All Colombian, no matter the colour, is #4. Mexican Mud, the granular brown heroin of the 70s and 80s was also #4. Today, most brown powder from Mexico though is Tar, converted into a powder.
Tar came into existence in the very late 70s/early 80s from Mexican producers who found it difficult to obtain all the needed chemicals.
Most people believe Tar to be acetylated opium. In other words, the believe the "cook" skips steps 2 and 3 of a 4 step process, simply taking raw opium, adding a glacial acetic acid and heating it. This is false.
Opium on average has a 10% content of morphine. The highest content ever recorded in lab grown poppies was 27%. IF ALL poppies had 27% morphine, Tar could have at most, 27% purity. Of course there is some Tar with a purity as high as 84/85% Acetylating opium will not increase the active content.
If you examine another form of heroin that falls outside the numbering system you will begin to understand the nature of Tar. "Home Baked" is a form made in New Zealand made from codeine (demethylated into morphine), morphine or when it existed, Diconal. Its consistency is exactly like Tars. Its constituency is exactly the same as well (MAMS 3 and 6) and so one can easily see how Tar is made (if they care to learn about the Home Bake process).