Turning an Aspen Burl
I have not had many aspen burls lately but one recently arrived and here it is before and after trimming and mounting on my lathe. The top bark part of the burl was attached to the head stock of the lathe. This will give a round bark edged bowl. Aspen burls usually have some decay inside so this was the safest choice. The log side of the burl was solid so it should provide a stable tenon for reverse mounting and hollowing.
Aspen burl is tricky to turn due to decay, grain separation, and soft punky regions that lead to holes. The next images show the turned profile and tenon base of the bowl. This part usually works well since the decay is typically inside the burl. However, these images show some grain separation and small holes. It is important to fill these using thin cyanoacrylate (CA) glue and coffee (espresso dark roast finely ground). The coffee fills a hole, crack or grain separation and the CA hardens it instantly. Ground coffee is a catalyst for activating the CA and it sands to a smooth dark color. I also use CA to harden the entire area just under the bark. Weak spots and holes around the bark can also be filled/hardened using the coffee trick. This process is important since it is likely there will be problems during hollowing.
The following images show the hollowing process. It is best to keep the bowl wall a bit thick, say ⅜ to ½ inch, since it is likely there will be weak areas in the wall. You can see the holes and decay in these images. There was also grain separation that shows in the third image. I use thin CA to stabilize such areas and all areas just under the bark as the hollowing progresses. I have had burls like this fly apart, but that is rare and was not an issue with this bowl. As a side note, in cases where the cracks might cause breaking, wrap the outer part of the bowl tightly with duct tape or plastic wrap and use coffee and glue in the opening cracks. Also, do not turn at high speeds. For this bowl I never exceeded 500 RPM! I also used over 2 oz of thin CA so make sure you have a lot on hand.
The next images show the completed bowl. It measures about 10.5" in max diameter, 9" high, and the wall thickness is about ½ inch. This wood is quite wet so the bowl needs to dry. I monitor the drying process by weighing the bowl every week and by observing it frequently. If any cracking happens, I use the CA/coffee process to stop the crack from growing. Cracking is most likely during the first several weeks. I also dry fresh turned bowls in a stable environment with temp in low 60's and humidity between 60 and 65%. It is important that temp and humidity do not change quickly. This bowl will take at least 2 months to dry. Sanding and oiling brings out the real beauty of aspen burl. I am always blown away as oil is applied to a sanded bowl. I use a pure tung oil - citrus solvent 50:50 mix (Real Milk Paint Company). I will add photos of the completely finished bowl.
Below are photos of the finished (sanded to 400 git, oiled with pure tung oil, and waxed with beeswax in walnut oil).
This bowl is for sale in my store on this web site.