How to Flame Polish Acrylic (Perspex)
Polished edges on acrylic look fantastic but professional diamond edge polishers are very expensive. If you have access to a propane or preferably MAP gas torch you can achieve very good results with some basic equipment and a little technique.
The most important thing to do before flame polishing is to prepare your edges. Any marks already on your edges will be much more visible after flame polishing. Saw marks can be removed in a number of ways.
Our preferred way in the workshop is to run the acrylic through the router table to remove between .25 and .5mm. A very sharp router bit will remove all saw marks and leave a wonderfully smooth finish ready for flame polishing.
If you don’t have a router or if the acrylic is of a shape which cannot be put through the table (say an acrylic box you have just made) then you can remove saw marks with a scraper. A new, sharp blade from a utility knife works well. Simply hold the blade crossways to the edge of the acrylic and at a slight angle and pull back towards you. You will need to continue until all visible marks disappear. You can also file or sand to remove marks.
Be careful also when handling the acrylic as finger prints and other marks will be burned into the acrylic once it is flamed. Wear cotton gloves when handling and ensure all dust and other marks are cleaned off before flaming. You will also need to remove any paper or plastic masking. Best to avoid cleaning solvents as they can go cloudy when flamed. A 5 parts water to one part methylated spirits can be used as a cleaner but make sure acrylic is thoroughly dry before flaming.
When it comes to flaming you need a very hot, pointy blue flame. MAP gas is best because it burns hotter but you can get good results with propane if that is all you have.
Bring the blue pointy (hottest) part of the flame in contact with the acrylic edge and move steadily along the edge. Keep moving and do not concentrate the flame in one spot. If you go too slow the acrylic can catch flame and if you go too fast you wont really polish the acrylic – it will look matt as opposed to glassy. If you have gone too fast wait for the acrylic to cool right down and repeat the process.
It is not uncommon, particularly with thin acrylic, for it to warp during this process but amazingly it will go back to its original shape when cooled.
Properly flamed polished acrylic will look like glass – perfectly transparent and smooth.
Good luck.Back to Tips of the Trade