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Como fazer acabamento boleado na garrafa pet passo a passo (This video is in a foreign Launage, but shows you how to make the cut edge of a plastic bottle curl to the inside making the top nice and smooth)...
here it is! how to give the perfect finish to a recycled bottle. The video is in Portuguese but very easy to follow. Note that the tin you use you will not use again to cook. Enjoy!