Re: Investing and Bubbles


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Posted by bruce paul fink on March 14, 1999 at 20:32:28:

In Reply to: Investing and Bubbles posted by Dan Caster on March 14, 1999 at 19:55:41:

There hopefully will be a number of solution directions coming in to follow this as each caster often has his own methods.

Here are a few to start the list:

#1 Allow the wax to soak and float in a tub of water until ready to invest. Use old water and if in the sun, that can be good, just cover the floating top with a rag to osmose the moisture and keep the sun off the wax. This starts an algae growth and this is better than anything I have found to break the surface wax to water tension. Rotate to another side daily. Sounds odd maybe but this is from years of experience and discovered since I would have hot summer days and fragile waxes and need a way to store them before investing while not letting them get saggy or softened and bumped.

#2 I would always add a plaster retarder and pre mix it in the water so you can get an idea of it's proportion potency and time allotment for each batch. I will address this as though it takes several batches to fill the entire mold but if not, you will just find this even simpler.

The setting time is determined by a number of variables so try to be as consistent with each batch so you pre-know your results and time slots.

So setting times are faster IF:

the proportion of retarder is greater...

the water is warmer than...

the water is greater in proportion to the mix than...

the mix is aggitated more or faster or longer than...

the time allowed to set and to mix it is greater than...

the plaster is aged more than... (sometimes evident by small hardening clumps in the plaster bag.)

And like that.

So... first try to fleck on a surface mix either by hand or by air spray gun or by commercial plaster hopper spray gun but DO add more of the retarder to this mix and keep it fairly stiff so it will at least grip or hold on without full running or sagging off.

Now with the still unset plaster investment surface hanging on pour the mixes into the container via a large 3 or 4 inch diameter PVC type pipe so there is no additional bubble aggitation in that process and start to fill the whole mold. Raise the pipe as neede to keep the bottom out of any setting layer. If doing a larger piece you will want to be sure the first or second layers are setting up to additionally hold the wax in place and not let it float later.

As you are continuing to pour the investmet mixes in, the last mix or two should have started to set and further hold the wax in its same location. Also the surface mix is still slightly soft and able to protect the surface from new pouring bubbles.

Keep pouring batches in til above the wax body part and then stop to allow a further set before finishig it off to the top.

Sound complicated? Sound like a commercial for ceramic shell? Only because this is in writing and when doing it it becomes second and natural nature. Just think of yourself as a wax that is allergic to investment bubbles and then do what you need to do to avoid them.

The Zen for the Day.

Now let's see what others have to offer as there has to be many other solutions as well. bpfink

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