Last week I found an article on Ganoksin about methods for addressing residual ash when casting 3D prints. I also found this forum post.
I’d like to start a discussion about addressing the specific issue of residual ash and looking for solutions. I’m envisioning this thread as a positive place to share information about what’s working and what’s not working with regards to surface quality of cast pieces…not as a place to air grievances, but for anyone who wants to participate and share information that will help everyone achieve better results.
Variables
Relevant information would include:
- Your kiln/burnout setup
- What resin you’re using (Formlabs or other)
- How long you allow your models to bench set (model in the flask with investment before burning out)
- Whether you’re curing the models
- Type of metal cast
- Casting setup (vacuum, centrifugal, or other)
- Flask sizes and type (perforated, solid)
- Final casting temperature
- Gram weight of your models
- Type of jewelry (heavy, prongs, filigree, etc).
I know a lot of jewelry folks have had issues with crusty-looking castings, and although we sometimes talk about porosity, I believe that it’s related to ash. In my experience placement of the defect is almost always at the bottom of the model, as if the ash is sitting in the bottom of the mold. I’ve tried blowing in the mold before casting, and also burning out with the button down, then turning it up in the last half of the burnout schedule.
Supposedly the larger companies and some casting houses have it figured out. But they are also reluctant to share techniques and information with anyone, including manufacturers of equipment and resin. Suppliers such as Rio Grande and Stuller are doing their own testing, and much information is scattered around the internet and in some cases contradictory.
To Vent or Not to Vent?
I just got off the phone with Orton, a company that makes a lot of controllers for kilns and a venting system, and had an informative discussion about their Ventmaster product and how it might be a solution to the residual ash issue with casting resins. Apparently it’s across the board with all manufacturers of castable resins and not specific to any particular Formlabs product.
Basically, he mentioned that a small 1/8" hole is drilled in the top of the kiln that facilitates air flow through the kiln to provide additional oxygen, and there is a second 1/8" hole drilled near the bottom which also has a collection cup. There is a blower attached, and this provides airflow to the kiln. Their Ventmaster solution on their site is listed at $520 USD, but I found the same kit on other sites for less (just Google). Not cheap, but considering the price of precious metals and resin, could be a worthwhile option if it works. (As a smaller-scale jewelry artist, I use a smaller kiln than the one shown in the picture for burnout…)
(Click to visit Bailey Pottery).
As we’ve all talked about residual ash, it seems that the solution centers around increased oxygen in the kiln (although one article said that even increased oxygen won’t address it, although Orton and others say it should). According to Ransom & Randolph (R&R), the manufacturers of Bandust investment, higher temperatures can prevent oxygen in the firing environment and the result is incomplete burnout of ash. BlueCast had recommended a burnout of around 1450°F, but R&R had stated specifically that the higher temperature would cause incomplete burnout because of the lack of oxygen.
Apparently adding a venting solution is an approach used in the ceramics community to assist with burnout of organic materials during firing. I asked if there are any jewelers using this solution to address residual ash, and he mentioned a large, somewhat local jewelry company that is well-known to me for making sculptural sterling silver jewelry in the same style that I make.
There was also a secondary part of the conversation that involved a product that they have that can determine the ideal burnout temperature…my guess is that the cost is prohibitive, but it might be worth seeing if we could pay someone to run an independent test? I would guess Formlabs has done something like this, but it would be interesting to get a third-party opinion.
My guess is that casting houses are using some sort of venting solution that smaller artists don’t have access to, or just don’t know about. I am considering purchase of the Ventmaster setup to use with my new Paragon Xpress burnout kiln.