Sintering problem? (Prometheus White Bronze)

[Chillikat]

Hello all,

When fired, should white bronze be bendable? Obviously stiff and solid is a given, but should it snap at a weak area or bend?

I fired a piece and, when putting some pressure on the bail to check the strength, it snapped off.
If it was just too thin, would it have bent rather than snapped?:



I followed the instructions to the letter - 15 mins at 500 degrees C on coconut carbon in a stainless steel container, then 2 hours at 770 degrees C with a layer of carbon on top and the lid on the container.
Any help would be appreciated,

Thank you in advance :-)

[Dennis]

Fired clay is brittle and porous. if you want thin parts to be more resistant to fracture, you must anneal them.

Quote from the online instructions:
Annealing: If your pieces are thin and long, then it is recommended that you anneal them in order to maintain high strength and malleability.

(Heat until the metal just appears to glow in a darkened room. Allow to cool a little, then quench in warm safety pickle, or alum solution and leave for two or three minutes, or until clean looking.
Neutralise in hot bicarbonate or soda crystal solution, rinse in plain water and brush up with a soapy jewellers brass brush.) Dennis.

[Chillikat]

Thanks Dennis - though I did in fact do that, I forgot to mention it! The instructions said to heat at 565 for 5 mins and then quench; which I did...

[Dennis]

Thanks Dennis - though I did in fact do that, I forgot to mention it! The instructions said to heat at 565 for 5 mins and then quench; which I did...

Well I haven't used that particular clay, but my experience is that quenching metals when red can cause them to weaken or collapse.
Time for some experiments I guess. Dennis.

[CJ57]

I think we are all as in the dark as you. There have been a couple of questions about bronze clay recently and none of us have used it. Not a lot of clay used by the regulars on the forum and I'd be quoting from the instructions like Dennis. Have you tried one of the forums specific to clay or the companies are usually quite good at giving advice?

[Chillikat]

Ok, thank you Caroline!

I read on one particular website that there is a bit of a conflict going on - the carbon that is used to reduce the oxygen around the piece to prevent oxidation has the negative effect of preventing the binder burning off; I think I will experiment with extending the timing of the first stage - I'll leave it longer for the binder to burn off before going into the carbon for the sintering.

I shall report back!