Can Alginate be used to make a mold from oil based clay sculpture?

Hi I have made a relief sculpture from oil-based clay and I wanted to know if I can make a mold using alginate. I've only ever used alginate to life cast before, but I'm hoping it will work with oil based clay. Also I don't know if the clay has sulphur in it, if that makes any difference. If it is possible, would be best to reinforce the alginate mold with plaster strips as one would in life casting? Thanks for your help!!!

Alginate will work just fine on any clay. A mother mold with something like plaster bandage would be recommended. Just keep in mind that, because it's alginate, you're going to get some shrinkage, and the mold won't last long.

Sweet! Thanks for your reply! I appreciate it

What do you want to cast the new positive in? With an alginate negative, you'll only be able to cast water based materials, i.e. plaster. Urethane resins will not work, nor will any epoxies or fiberglas positives....

Grab some smooth-on mold max 30 silicone, zero shrinkage, easy to use and will last for many castings.!

Mostly Fantasy said:

What do you want to cast the new positive in? With an alginate negative, you'll only be able to cast water based materials, i.e. plaster. Urethane resins will not work, nor will any epoxies or fiberglas positives....

Click to expand...

It is true that alginate does not work well with PU resins as it carries a lot of moisture. But with a work around it can be done.
Swirling acetone in the alginate mold, this helps to draw out some moisture. After that spray the mold surface with a fast setting spray paint (the kind used for automotive use, no other) to seal the surface. You can also try to slightly warm up the surface of the mold with a hair dryer previous to all this, but little and careful to prevent shrinkage.
After all this you can go with the resin. A faster setting resin (like smoothcast 300Q ) can help to prevent moisture getting in the process and avoid foaming. But I´ve used other resins too.
I´ve used this method applying the resin by layers and reinforcing it with poyfibers or fiberglass or filling it (the resin layers) with rigid PU foam.
Some foaming can happen (probably it will not be so hard a as a resin used in a dry silicone mold) but in my case it hasn´t been a problem for what I needed the pieces.
Never tried it with full resin castings. always layers.
Not perfect but it can do the trick depending on the use.

I already cast my sculpture in plaster, as that was my material of choice because I had to recreate a stone relief and I knew I could paint plaster convincingly and also I have never worked with resin and it didn't seem like it would give me the texture I needed. Also plaster's cheap and I knew through experience it would work. But I was gifted a big box of alginate from a professor a while ago (which is why I was using alginate in the first place), so I still have a bunch of it left over and I'll definitely experiment with the methods you described to cast with resin. I really appreciate your detailed comment because I thought I was limited to only plaster! Thank you everyone for your replies I appreciate it.