Delft clay casting troubles - air bubbles and incomplete castings

[joshd1410]

Hello! I purchased the delft clay casting kit a couple of weeks ago and have had a few goes with it since. For the first few attempts I accepted that they wouldn't be perfect and this was fine but 2 weeks on and I still haven't had a single successful cast. So far the two main problems I have come up against have been that the mold will not properly fill up before the silver hardens resulting in an incomplete casting and even on the incomplete casting there are small cavities which I can only assume were air bubbles. Most of my attempts so far have been at casting a guitar pick (about 25x30x2mm) and only once has the mold filled up completely. Every other time the silver seems to harden far too quickly. I have been creating plenty of air vents and making the pouring hole around 5-6mm every time.

Does anyone have any suggestions/tips for me? I've watched several videos and feel like I've had enough attempts to at least be getting full casts by now but I'm getting slightly jaded with it now as the time it takes to prepare the mold seems wasted if it's not going to work. Does the mold need to be heated perhaps to keep the silver flowing a little longer and if so how is this done? Thanks for reading and for any advice you might have!

[Dennis]

Make more vent holes, use more flux, keep a flame on the scorifier when pouring. However, this method is only suitable for thin objects, like coins. Dennis.

[joshd1410]

Thanks. What type of flux is best to use?

[Wallace]

borax powder is you friend when it comes to casting

[china]

As said above Borax powder the same as you would have used to glaze your crucible

[MMM Jewellery]

Hi
I have done a lot of delft casting- not always successfully! It is easier to start with something a bit thicker (eg two picks together) or to carve channels in the top layer of sand so that heat is not lost so fast, and molten metal can reach all parts of the cast. I have also used two sprue channels eg for a ring so that one goes to the main bulk at the front of the ring, and a second goes to the back of the thin shank to provide molten metal there. Also over-heat your metal a bit so that it stays molten longer. When I cast leaves I would build up the back with wax to get something thick enough to cast. Keep at it!
Cheers Matt

[joshd1410]

Thanks for all the replies. I had toyed with the idea of multiple channels. How do you execute this exactly? Do you do two seperate pours, one in each channel or do you link both channels up so that one pour will travel down both channels at the same time?

[MMM Jewellery]

You will need it to go down both at once.

[enigma]

2mm is very thin for delft casting.