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  #1  
Old 03-21-2003, 05:16 AM
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obseq obseq is offline
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preparations for casting

i am in the process of creating the plaster models for what likely will be bronze pieces for my installation.

i was wondering what methods would be best for these plaster versions?

i have a bit of an idea but i wanted to see what those of you with vastly more experience think.

A) i am transfering the digital images that i will cast to scale prints

B) from that information i am going to use cardboard or some (other malleable veneer) as a basis for the shape. (what do any of you suggest for reinforcement to these pieces, rebar, etc...)



C)from there i will apply the plaster, leaving me with "shells" or "plate-like" pieces.

so, what would be the next step in taking these casts to a foundry?????

should i bother with algenate?(sp?)


i realize that this is fairly vague without any images to supplement my description....


*any* and *all* suggestions are truly appreciated.


thanks in advance
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  #2  
Old 03-21-2003, 11:23 AM
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JHoughton JHoughton is offline
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Re: preparations for casting

Quote:
Originally posted by obseq
i am in the process of creating the plaster models for what likely will be bronze pieces for my installation.

i was wondering what methods would be best for these plaster versions?

i have a bit of an idea but i wanted to see what those of you with vastly more experience think.

A) i am transfering the digital images that i will cast to scale prints

B) from that information i am going to use cardboard or some (other malleable veneer) as a basis for the shape. (what do any of you suggest for reinforcement to these pieces, rebar, etc...)

C)from there i will apply the plaster, leaving me with "shells" or "plate-like" pieces.

so, what would be the next step in taking these casts to a foundry?????

should i bother with algenate?(sp?)

i realize that this is fairly vague without any images to supplement my description....

*any* and *all* suggestions are truly appreciated.

thanks in advance
It is either too early in the a.m. for me or you are very vague in your descriptions.
1. First of all are the plaster models as you call them goint to be the actual postitives you are to mold?
2. What is meant by casting to a scale print?
3. If you are going full scale rebar or 1/4 hot rolled rod is what I would suggest as plaster and mold making material can put a lot of stress on an armature.
4. By plate-like shells do you mean that the mold is plaster and takes on the shape of the cardboard/vaneer material? Is the form digitized (meaning that it is geometric and not organic in nature?)
5. If the above is true then you will need to cast wax into these plaster negetives to have a commercial foundry or school foundry shell them up and cast them. Not to metion the welding, chasing, and patination.
6. Alginate is beautiful for highly detailed applications like faces, hand, and feet. Alginate molds are most generally waist molds as they dry and break up unless kept wet.
Hope this is of some help to you, if you are not independantly wealthy or have a grant it is not something to go into lighly. Lotsa luck
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J Houghton
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  #3  
Old 03-21-2003, 09:28 PM
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Re: Re: preparations for casting

Quote:
Originally posted by JHoughton
It is either too early in the a.m. for me or you are very vague in your descriptions.
1. First of all are the plaster models as you call them goint to be the actual postitives you are to mold?
2. What is meant by casting to a scale print?
3. If you are going full scale rebar or 1/4 hot rolled rod is what I would suggest as plaster and mold making material can put a lot of stress on an armature.
4. By plate-like shells do you mean that the mold is plaster and takes on the shape of the cardboard/vaneer material? Is the form digitized (meaning that it is geometric and not organic in nature?)
5. If the above is true then you will need to cast wax into these plaster negetives to have a commercial foundry or school foundry shell them up and cast them. Not to metion the welding, chasing, and patination.
6. Alginate is beautiful for highly detailed applications like faces, hand, and feet. Alginate molds are most generally waist molds as they dry and break up unless kept wet.
Hope this is of some help to you, if you are not independantly wealthy or have a grant it is not something to go into lighly. Lotsa luck

jarrod,

thanks for the input.

sorry again for the vague description....hopefully i can clarify some of the things you pointed out.

basically, i began with a photograph of a face.

i then digitized this image and edited it in photoshop, acheiving the desired image i need, which is basically 3 seperate "pieces" that make up the face in silhouette.

from the final digital form i will print up copies of each "piece" to the scale that i want the physical casts to be.

so, in essence the three pieces will be flat with varying degrees of concavity.

my main concern is how to proceed with materials with regard to the initial casts..

unfortunately, i am not independantly wealthy or have a nice grant to supplement my work, however, i do know someone who can grant me nearly free access to a foundry and very cheap materials.

thanks again.
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  #4  
Old 03-23-2003, 06:29 PM
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JHoughton JHoughton is offline
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Quote:

so, in essence the three pieces will be flat with varying degrees of concavity.

my main concern is how to proceed with materials with regard to the initial casts..

If I have this correct in my mind, you hould not need alginate as you are not reproducing human flesh or very tight details in the casts... Right?

You intend to make the positive pieces out of cardboard or plaster and then mold them to cast.

If you are adept at greensand or bonded sand casting you can do them fairly easily with out making molds as the sand takes its (the molds) place.

If not, you will most probably use ceramic shell to cast them. This requires you
to make a mold and reproduce the positives in wax. If I am helping and you wan't any more info feel free to post replies or to e-mail me.
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  #5  
Old 03-23-2003, 10:53 PM
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fritchie fritchie is offline
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Lightbulb

Let me follow up with what may be even simpler, if I understand your objective correctly. I understand that you are taking a 2D outline (silhouette) of a face, cutting this into several pieces, and that you want to make bronze replicas of the pieces.

If thatí what you are doing, the cheapest thing probably will be to make your traces (in the exact size that you want) directly onto flat sheets of casting wax, whatever thickness wax you want, cut the wax into your shapes, and then help the foundry make molds and casts from the wax. That way, you have no intermediate cardboard, etc., and no extra molds to make. Did I understand your objective correctly?
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  #6  
Old 03-24-2003, 10:10 AM
Toby Toby is offline
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Casting feedback

I've been casting stuff in aluminium these last few months, there are a few pointers I can offer.

Doing the master in plaster may be tricky if you want to get a mold off it again. Lots of undercuts = lots of grief and multiple piece moulds.

Over here in Dublin the art foundrys generally take anything and produce the investment molds themselves so you don't have to worry: give them a call.

Another process is to make a flexible mould (Vylamold or RTV silicones) supported in a plaster shell which gives reasonably good detail. Produce a wax image, add on sprues, gates and all the wearisome network of pipes for molten metal to go in and air to get out. I use sticks of wax and a hot knife to do this. Further detail is required and if you're still interested I can elaborate.

After going to all that trouble you could probably do the ceramic shell or plaster investment yourself. I don't have experience with ceramic shell, but plaster investment is just a 50/50 mix of casting plaster and fairly fine (+ clean sand). One is supposed to be able to use bits of fired clay mixed in too (crank) but I got 2 cheap bags of sand and they get reused.
I tend to use wire mesh reinforcing in the investment, it seems to get quite brittle after burnout. The plaster walls gotta be at least 2" thick, the stuff really loses strength after firing. I would ask your foundry what they expect.
The wax must be melted or steamed out (I reclaim the wax using a boiling tea caddy and a length of silicone tubing + duct tape). If you want to melt it out in a kiln, this is quite an antisocial activity and buggers up the elements in an electric kiln. I have torched it out but it leaves soot. The plaster MUST be baked at 600-650 centigrade. Drives out 'chemically-bonded' water which would otherwise turn to steam when you're pouring the metal and jets the molten metal out again. Not good.
Theres quite a bit more background on sites like backyardmetalcasting.??? Note that Aluminium melts at 1/2 the temperature of bronze and is consequently that little bit easier to manage - take that as a warning and a disclaimer. That said, I feel a little more professional than the nutters pouring aluminium in their carpet slippers out of old baked bean tins.

Alginate: Expensive, good for sensitive areas like face and hands, the normal-set variety is workable for a nightmarishly short length of time. Use pre-measured cups and prepare to curse.
LATEX is a good alternative for larger less sensitive areas of skin. Remember to test for allergies + use vaseline ( petroleum jelly) on hair. Use latex thickener to brush on a decent coat.

If expanded foam can be used as the sculpture medium, this is a joy to cast as it just dissolves under the metal (sprues still needed in plaster investment)
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  #7  
Old 03-24-2003, 10:24 AM
Toby Toby is offline
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Talking Woops, didn't read the whole thread..

I've just read the bit about what you're making..
This means you don't need sprues or risers as you can just pour the metal into an open cavity made from an impression of the original (note metal will shrink slightly in centre on the back). Providing the sides of the positive image have a slight taper, you should'nt need flexible moulds and you can make a plaster investmest straight off. Maybe put a layer of heavy mesh in the back. You can use vaseline diluted down with white spirits as a mold release agent. Don't forget to bake the thing before pouring the metal. Polystyrene sounds really feasible. Remember to wear your leathers when pouring metal.
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  #8  
Old 03-24-2003, 11:22 PM
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fritchie fritchie is offline
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flat originals

The last idea gives me a cheaper suggestion than my earlier one. In the US, I think casting wax is a little over $3 per pound in bulk (ca. 50 pounds) but the foundry probably could let you have just the amount you need. If you can get sheets of foam the thickness you want, they might be cheaper. If you want a flat surface instead of the irregular foam surface, you can paint warm wax onto the foam pieces and melt (gently!) With a hot spatula or clothes iron.

As Jarrod said, if these really are flat pieces and you donít need extremely fine detail, casting into a sand mold would be much cheaper than investment or ceramic shell. Iíve never seen sand casting myself, but the procedure as described couldnít be easier or cheaper. With investment or ceramic shell, you need to add sprues and vents (channels for wax/foam/air to exit and bronze to enter). The foundry can better explain these by example.
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  #9  
Old 03-25-2003, 03:50 AM
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Re: flat originals

Quote:
Originally posted by fritchie
The last idea gives me a cheaper suggestion than my earlier one. In the US, I think casting wax is a little over $3 per pound in bulk (ca. 50 pounds) but the foundry probably could let you have just the amount you need. If you can get sheets of foam the thickness you want, they might be cheaper. If you want a flat surface instead of the irregular foam surface, you can paint warm wax onto the foam pieces and melt (gently!) With a hot spatula or clothes iron.

As Jarrod said, if these really are flat pieces and you donít need extremely fine detail, casting into a sand mold would be much cheaper than investment or ceramic shell. Iíve never seen sand casting myself, but the procedure as described couldnít be easier or cheaper. With investment or ceramic shell, you need to add sprues and vents (channels for wax/foam/air to exit and bronze to enter). The foundry can better explain these by example.


wow guys,

this has been a HUGE help....

I went ahead and printed out the thread.

i cant believe i didnt think about the expanding foam yet.....this might be feasible. does this type of foam have a name????

i realzied algenate will be very costly and perhaps superflous where detail is concerned. i molded my own body with using algenate once....tricky, tricky stuff--but--the results are pretty incredible


i did manage to find a link of an artist, gillian jagger, who cast parts of dead animals (including her horse). the general thickness, texture, and variances in concavity of each seperate piece is what i am aiming for .i've attached an example of her work to the post as an example of what i am aiming for. her pieces are in plaster, however.


jarrod, fritchie, and toby thanks so much....


im sure i'll be bugging you all with more questions as i progress!







thanks again!

Last edited by obseq : 11-17-2008 at 08:40 AM.
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  #10  
Old 03-25-2003, 02:10 PM
Randy Randy is offline
 
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Hey!

Didn't we see this piece in Sculpture Magazine recently???
Randy
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  #11  
Old 03-26-2003, 02:07 AM
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obseq obseq is offline
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Re: Hey!

Quote:
Originally posted by Randy
Didn't we see this piece in Sculpture Magazine recently???
Randy

yep! indeed we did....it was in the september issue....

my circumstance in discovering it is twofold.


first and foremost i wanted to find an art periodical that had a more scholarly approach in what it featured. sculpture was the best i have read thus far.

second, i had to buy the issue of with the jagger article because i found that her presentation of that specific piece was in line with what i had in mind for my installation, so i bought it immediately, rather excited.
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  #12  
Old 03-26-2003, 05:08 PM
Toby Toby is offline
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Lightbulb interminable ramblings..

Still thinking about your thing.
If theres oil-bonded sand in your art foundry and a suitable box, I reckon you can just tamp and ram the sand around your positive. Usually faster than waiting for plaster to bake.

Heres a thought. If one side of your piece is facing the wall, or is just flat, you don't have to have it covered. Essentially you just leave the mould open and fill it up like a jelly mould. No sprues, risers, maybe a channel for pouring the metal into it.

I find the detail of polystyrene (aeroboard, expanded foam..) is not noticable using sand. Also find that a 5" angle grinder with a grinding wheel and cup brush does an easy finish. Bronze is fairly soft.

You can do the thing in plywood as well in an open mould (course, you've got to lift the plywood out before pouring)

To be honest I found that after trawling the internet and extracting information from fellow artists, I have a reasonable setup that will melt 10 kilo of aluminium a go which set me back about $150 all told. I find melting bronze in the same setup a bit trickier and I'll need a ceramic crucible. Theres a lot of demystification involved in casting. Toby
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  #13  
Old 03-26-2003, 05:50 PM
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Face in aluminium

Here's a face being broken out of an investment mold, pouring cup still attached to forehead, alginate to wax positive
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  #14  
Old 03-27-2003, 03:25 AM
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obseq obseq is offline
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Re: Face in aluminium

Quote:
Originally posted by Toby
Here's a face being broken out of an investment mold, pouring cup still attached to forehead, alginate to wax positive

toby,

here is the original image i am working with....as you can see i will be working with 3 distinct pieces.....

im still really curious about the exapning foam you described.

is it expensive?

fortunately i wont need any alginate as such detail would be superfluous for my purposes.....i was tinkering with the idea of an open mold as you described in plywood but would prefer if i wasnt left with one flat side to each peice.


your aluminum head looks impressive! thanks for posting it!

Last edited by obseq : 11-17-2008 at 08:40 AM.
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  #15  
Old 03-30-2003, 12:51 PM
Toby Toby is offline
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Expanded foam, open moulds

Expanded polystyrene is marketed under a variety of names in a range of densities (aeroboard, styrofoam, polystyrene). Examples are the wee bits of loose packing in cardboard boxes, the stuff you get around refrigerators and computers when you buy them new, disposable foam cups. The car manufacturers use expanded polystyrene moulds for making things like ehgine inlets and complex castings. They literally pack sand (oil bond or petrobond) around these things, pour aluminium in, and shake off the sand. You can sometimes see the marks of the styrofoam left on the casting. This is well handy for them for making hollow sections, otherwise they'd probably use a steel mould.
The stuff can be purchased for builders supplies as cavity wall insulation in 2" thick 4'x8' sheets. I've found that the glue to effectively laminate this stuff togther is a bit pricey and I'm thinking of switching to caesin, animal-based or rabbit skin glues. (I used an evostick contact cement that was designed not to melt it)It can also be bought in big blocks here but is harder to track down. The stuff can be shaped with hot tools, heated nichrome wire, sanders, electric carving knives... this is what most people get up to in making film sets.

If you dont want a flat back to the sculpture you'll have to either cast it in two pieces and weld or bolt them togther or alternatively use a closed mould. I think I should also mention that if you intend the thickness of the sculpture to be over an inch anywhere that you should probably make it hollow. This saves metal, weight and makes for more reliable cooling of the metal.

I'm beginning to think that you might be best off producing a wax positive (from looking at your photo) and that using a RTV vulcanising silicone would produce a decent mould from your original positive. If you have access to a school studio, you might find some, or some vylamould. I have heard rumour of mixing builders silicone with washing up liquid as a cost effective substitute. Anyone else out there tried this?
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  #16  
Old 04-04-2003, 12:36 AM
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obseq obseq is offline
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ive sent you another question via pm just to avoid cluttering up the main board...

thanks again..!
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  #17  
Old 04-28-2003, 01:30 AM
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update

well,

i've forged ahead with everything in the past few weeks...


unfortunately, i've been held down by a strict budget, so as a result i've been mired in a yeoman's effort. :

i went ahead and printed out to-scale 2-D images of each piece, with each about 2ftx3ft. i taped each individual sheet of paper together totaling ~100 sheets....

from there, i proceeded with quite a bit more clear masking tape on both sides just to lend the composites some rigidity. i bought some automotive rubberized coating which i applied to the back of each composite. this worked quite well at $4.00 per can and added nominal thickness as well as durability. so now, after yet another visit to the hardware store, i am left with each composite coated in high-resin polyeurathane coating for hardwood floors...

to the delight of my wallet and my creative sanity this worked well....each composite is almost completely rigid but i'll need to add some additonal coats.

so....from there i've purchased a heat gun to shape each composite how i wish; making sure everything adheres to the original image....




next step: plaster veneer before taking them to the foundry.

more later...

Last edited by obseq : 11-17-2008 at 08:40 AM.
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