Cleaning up ceramic shell

[gpiper]

I recently did a test pour at home and all went well. My question though is: when applying the first layer of ceramic shell using the zircon sand, does the quantity / proportion of the sand in the mix affect how easy it is to get the hardened shell out of small crevices? In the test, I deliberately did some finer details to see how it would go, but getting the shell out of these places is a bit of a mission, despite using dental-type tools.
So, is more sand more likely to make this first layer easier to extract later?

[olivier]

Glad it all went well... In fact, I am thrilled it all went well... Great testimonial for the book !

Removing bits of shell from the metal can be a mission. The longer you wait the harder it gets. Best to clean the casting as soon as possible.

Vigorously hammering the button will make the metal vibrate and make most of the shell come off in large chunks. No matter what, there will always be small to very small bits stuck in small anfractuosities and defects.

Some foundries are said to use acid baths to soften the ceramic. I did that once and never again… The acid will seep into the metal small pores and invisible crevices from which It will l continue to leech out for months, ruining all patina work in the process.

I used to spend hours picking up small bits while watching TV… Until I invested in a sand blaster… Even a cheap toy can turn a 5 days job into a 5 minutes job. I used to buy expensive glass beads to blast. I now use sand from the local beach.

I do not think that the amount of Zircon you apply will have any effect on the removal of the shell. I have heard that adding graphite powder to the slurry used for the first coat of ceramic will make removing shell bits easier but I have not found any substantial improvement with this method, or at least nothing as spectacular as using a sand blaster. On the contrary, graphite makes the ceramic darker and therefore more difficult to spot. (a quick liver of sulphur patina will darken the metal and reveal any leftover minute shell bits, but only if it is bright white.)

A sand blaster will clean your bronze quickly and thoroughly. If you are only casting very occasionally, this may be a superfluous expense… Find someone amongst your friend or neighbours… Many car electrical workshops have one for the purpose of cleaning parts of oxidation… They’ll let you use it for a beer or a song if you can sing.

I hope this helps.

[ww1aero]

Glad it all went well... In fact, I am thrilled it all went well... Great testimonial for the book !

Removing bits of shell from the metal can be a mission. The longer you wait the harder it gets. Best to clean the casting as soon as possible.
Vigorously hammering the button will make the metal vibrate and make most of the shell come off in large chunks. No matter what, there will always be small to very small bits stuck in small anfractuosities and defects.
A sand blaster will clean your bronze quickly and thoroughly. If you are only casting very occasionally, this may be a superfluous expense… Find someone amongst your friend or neighbours… Many car electrical workshops have one for the purpose of cleaning parts of oxidation… They’ll let you use it for a beer or a song if you can sing.

I hope this helps.

Hi Olivier,

I haven't worked with bronze yet, so I don't really have a feel for how soft or delicate the surface might be. I was wondering if cleaning the casting by scraping at the remaining shell mold particles might also scratch the bronze or if sand blasting might smooth out some details like skin textures or sharp edges? And if I'd have the same (or worse) problems with silver castings being damaged or loosing detail upon clean up.

Thanks for the information..............Pete

[olivier]

Hello Pete,

In my experience sand blasting has never damaged the bronze surface to any visible extend. I use some sand from the local beach. Works well.

As an indication, a light sand blasting does not affect fine details such as finger prints.

Even if there is no ceramic left, I still give a light all over blasting before applying the patina, it removes any greasy patch and the patina takes better.

[ww1aero]

Great, thanks for the information Olivier, I was worried about loosing detail, but if you can still see fingerprints, that certainly alays my fears. I didn't want to go through all the trouble of trying to cast and not even like the end results. I just ordered your Bronze Casting Manual (PDF), and I live close to Sean Colson (Shellspen) and might try his shell mold additive that makes the shell slurry easier to mix and keeps the particles in suspension while the slurry is waiting to be used.

Take Care.........Pete