Stephani Stephenson on sat 11 nov 06
Donald Wrote:
\I have tried mixing two types of plaster. A 50/50 ratio of USG no.1 and
USG Hydrocal white. I remember reading about this suggestion in Frank
Giorgini's Tile text. It is a tricky approach at best.
Hi Donald and all,
Interesting to read your experience
I have been using ceramcal ( consistency of 42 I believe) . It is
definitely more porous and less hard than hydrostone and I switched
over to it from Hydrocal as well
(Though there are a number of products out there so I wonder if it is
the same you are using. )
Another product I have tried recently is Durocal, which is on the
softer more porous end (consistency of 60) of the scale, but harder
and less porous than pottery #1 or Puritan.
(PP#1 around 70) It also has small inclusions of fiber, ( so tiny I
haven't noticed them).Durocal , they say, will allow you to get
significantly more pressings and especially will keep the detail from
wearing away so soon, while still remaining quite easy to carve.
Durocal is still somewhat too soft for my purposes, but it might work
for some seeking that middle ground.
As far as carving, I am able to true up, touch up the ceramical
after it cures , but I do it within the first few hours, as once it
cures it becomes
quite hard. also , a plug for Bison tools here....I have a couple that
work beautifully in this situation.
I have found ceramical to be quite useful in purge molds as well and
ram press molds.
There are also plaster additives which will retard the setting up of
the plaster. this I think is mainly to allow more time to model plaster
and may or may not prove useful in allowing for post curing carving.
I have combined different plasters on occasion though the products
have not been so far apart on the consistency scale as hydrostone and
pottery # 1... and usually it is when I have partial bags I need to
use up.
In general , on the question of process:
If I could take a step back from these numbers for a minute.
When you are learning to use plaster I believe it is best to be as
precise as possible. Weigh, measure, read about gypsum products.
observe, record, repeat.
do that until you achieve consistent success.
SO , though it may sound contradictory. Both the process and the
materials are both very precise and also quite imprecise.
The old timers make all kinds of adjustments. They vary the amount
of water water, they vary the mixing time, they do lots of things.
They know their products , they know how they will behave and they
know what they want. they know where they can push it and where they
cannot.
I would never introduce someone to the process by saying, here's some
preheated gypsum, here's some water, voila!
yet , on the other hand, that is all we are talking about here,
calcined gypsum and water!
So there's definitely room for variation on the part of the individual
with some experience.
Stephani Stephenson
steph@revivaltileworks.com
http://www.revivaltileworks.com
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