jonathan kaplan on sun 6 nov 11
Its interesting reading others journeys into slip-casting as many of us =3D
have taken that venture either out of necessity or out of making work =3D
that is primarily design based
and slip casting is the best way to produce that work. While I am sure =3D
that such a statement could ignite many a passionate discourse, I'll =3D
choose not to weigh in at this time.
Regarding Darvan products and sodium silicate, I would posit that we =3D
each find materials that work best in our particular applications and =3D
there really is no right or wrong. For me, I don't appreciate
the very exact measurements that are required using sodium silicate. It =3D
is so easy to over deflocculate a batch of slip with just a bit too much =
=3D
sodium silicate rendering it into a thixotropic ooze. Sodium silicate =3D
also discourages long mold life. Its caustic action on the casting =3D
surface yields an overabundance of surface degredation. Further, it =3D
promotes white fuzz on the exterior of the mold.
Darvan products in my application are more forgiving and have a wider =3D
range of usefulness than sodium silicate. If we reference a Bell Curve =3D
representing the deflocculation of a casting slip, the ascending left =3D
side of that curve starts with zero deflocculation and moves up that =3D
side being under-deflocculated. As it approaches the apex of the Bell =3D
Curve, we start being properly deflocculated with that top most point =3D
right on the money. Going down the right side we approach over =3D
deflocculation. Sliding down that side even further the casting slip =3D
becomes so overly saturated with deflocculant that it becomes =3D
thixotropic. Both Darvan products and sodium silicate can over =3D
deflocculate a casting slip.
Sodium silicate occupies a very small position at the top of that Bell =3D
Curve and it is a very small space indeed. Darvan 811 is a bit more =3D
forgiving and has a much larger occupied space on either side of the top =
=3D
of that curve. I can dial in my correct viscosity quite easily with a =3D
Number 2 Zahn Cup with small additions of Darvan 811, whereas if I were =3D
to use sodium silicate I would run a very dangerous risk of loosing that =
=3D
batch of slip. For me, Darvan 811 produces casting slips that are more =3D
giving and have a wider range of usefulness.
It is important to understand that this is just what works for me with =3D
my particular casting slips. I am sure that our partners in the ceramic =3D
industry would have entirely different methodologies Others on this =3D
list as mentioned in previous postings also have ways that work for =3D
them.
Respectfully
Jonathan
Jonathan Kaplan
curator
Plinth Gallery
3520 Brighton Blvd
Denver, CO 80216
www.plinthgallery.com
303 295-0717 =3D20
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