1) dissolve the cocaine base in ether (1gr of cocaine base per 15ml ether). Filter it to get rid of any ether insoluble cuts that remained from the ammonia treatment
2) dissolve 38% lab grade hydrochloric acid in acetone (0.25ml of hcl acid per 15ml acetone per gram of base
3) add the acetone/hcl acid solution in the ether/base solution. A visible white reaction will form, crystals will start precipitating in the bottom. When the solution is no longer reacting (it will be clear no white clouds), gently stir it, leave it for a few hours for the crystals to properly grow. Run the rod up the beaker, over carrying some liquid, if no crystallization happens you are good, its done. In any case leave it 3-4 hours to properly crystallize.
4) discard the ether (leaving the cocaine in the beaker!) and do a very thorough acetone wash in order to remove any traces of ether left. After a few pours of acetone in the beaker filter out the cocaine base (just like le junk describes nothing fancy). Perform a final acetone wash over the filter. Fold the cocaine in the filter and let it dry for a couple of days. Thats called an empanada.

voila cocaine as pure as it can get.

the other method (ether free) is done by dissolving cocaine directly into acetone. Then dissolving hydrochloric acid (38% lab grade) in methanol. You use 0.25ml of hcl acid per gram of cocaine base and double that of methanol i.e a 1:2 solution of hcl acid/methanol. You gently swirl both beakers by hand (like rotating them) and mix them, cocaine will start precipitating. After 2 hours stir everything and let for another 4-5 hours. Then filter out the cocaine acetone wash and let it dry.