Just to throw this out there, while that is an absolutely correct way to refine opium, there are more complex methods that yield a better product. With opium, you want to filter out as much STUFF as possible. A quick run down would be as follows:
Dissolve opium latex in water at a ratio of 1g to 10ml or thereabouts. Technically thats for poppy straw but latex works.
Heat to 60-80C, never going above 80 (70 would be ideal)
Let it "simmer" for 3 hours (it shouldnt bubble)
Strain through a non-paper coffee filter, cheesecloth, stocking, etc. Something fine, but not TOO fine. Thats later.
Fill plastic bottles roughly 2/3 full with solution and let freeze. Not all the way mind you, just until some chunks of ice form, then filter off the ice. Do it 3-4 times or until color starts showing in the ice.
Take some paraffin wax, barely get it melted, and add to the solution. Refrigerate solution (wax and all) until its cool/cold. Filter off wax.
Now, pass liquid through fine mesh bags (Im talking at least 10 micron here).
Let evaporate (never going above 80C if your heating it) and your done.
By the way, the freezing removes insoluble particles better than the filter, and the wax removes various plant fats and what not that filtering will not remove.
Labor intensive? Sort of. I mean really, all your doing is adding wax and freezing it, and filtering a bit more.
I also want to take the time to point out I did *not* write this on my own, I am in no way taking credit. I got it from another thread on another board that I have been a member of for a while. At least I didnt copy paste, I did paraphrase.
Regardless, its a method that works and yields a better product than almost anything else out there. Just depends if you want high quality or not.