[Jewelry making - Article 00005] - Re: [Orchid] Casting sheet silver

[jesse brennan]

========[ Invite a Friend - http://www.ganoksin.com/invite.htm  ]========


    Frank's answer is correct to a point. Plaster molds are a viable 
    technique used industrially. They are usually used for zinc and
    aluminum casting but occasionally are used for bronze and other
    copper alloys. I use them as cores in sand casting bronze as well as
    cores in ceramic shell investment molds. The Plaster  can be  molding
    plaster about 50-50 with fine sand or any plaster investment
    material.  I use   molding plaster with 60 80 mesh silica sand.
    Idealy you would use an entraining plaster mix but I haven't. The
    molds MUST be baked to remove  Water before casting and used quickly
    because the material will pick up water again after it cools. Molds
    for aluminum and other lower melting metals are baked to 400- 500 F
    to be useable. Molds for bronze and   higher melting metals ( which
    would include silver) are baked to  what would be normal investment
    casting burn out temperatures - 1200F  would be a normal maximum
    temperature but 900 F  would be OK and risk less damage to the
    plaster.  900 F wax burn outs cast in bronze have been found to be
    very satisfactory.  Your mold would  not have wax to burn out but
    the  900F temperature should be reached.   You  can expect some
    small porosity in what you are planing . Black discoloration on the
    surface if any  will be the result of breakdown  of the gypsum
    plaster - a sulfur compound.  Depending on the size the mold is very
    simple and will look like a small version of a mold to make wax
    sheets  for wax sculpture   to be investment cast in  bronze , or
    whatever.  Start with a flat non porous surface - wood, glass a poly
    cutting board or the like .   Lay a sheet of a similar material
    thicker than you want as big as you want on top of this and build a
    retaining box around this with a little space for a plaster wall to
    form. cardboard , tape or even plastiline works.  coat the  surface
    to be coated with a mold release such as Pam, vegetable oil, wax  or
    a silicone compound - I use silicone "tire shine"from an auto parts
    store .  Mix you  plaster mix. Pour in - let set.  Remove mold box .
    Turn over the mold and carve any details in the surface . Proceed to
     dry out the mold . The cores I use in bronze sand molds have only
    been baked out to kitchen oven temperature,and kept in a sealed
    metal can until use a few hours later- this is not ideal but if the
    core is vented well they work great.  In ceramic shell molds the
    core goes to the burnout and vitrification temperature just before
    pouring.These cores are also installed  so they re well vented to 
    get rid of any gas formed by the hot metal. These really work well
    at bronze temperatures.  I have reused this type open mold several
    times for pewter but at the higher temperatures they are considered
    one time use. You should have some experience with the casting
    techniques and the requirements for safe handling. jesse


____________________________________________________________________
T h e   O r c h i d   L i s t
Open Electronic Forum for Jewelry Manufacturing Methods and Procedures
____________________________________________________________________
Orchid FAQ:
~ http://www.ganoksin.com/orchid/faq.htm
Orchid Archives:
~ http://www.ganoksin.com/orchid/archive
Orchid Galleries:
~ http://www.ganoksin.com/orchid/gallery.htm
Invite a Friend:
~ http://www.ganoksin.com/invite.htm
____________________________________________________________________
Tips From The Jeweler's Bench - Article Archive
~ http://www.ganoksin.com/borisat/tip_sear.htm
The Jeweler's Selected Bibliography List
~ http://www.ganoksin.com/jewelry-books
Buy Orchid Jewelry:
~ http://www.ganoksin.com/shop
____________________________________________________________________
-Unsubscribe:
-Email: orchid-request AT ganoksin.com Body=unsubscribe subject=blank
____________________________________________________________________