repairing surface of cold cast bronze

[Santosh Yes]

I have made a cold cast bronze figure but I am having trouble repairing surface imperfections (where I had sand back small areas of the resin bronze surface to counter mold registration problems ). I have tried mixing bronze powder with resin and painting over these areas, curing and trying to sand level with the good bronze surface however this leaves a rough looking finish that doesnt match. I have also tried thinning the mix with a little acetone to get more bronze powder in the mix, also painting thinned resin first then dusting on bronze powder, but still havent got a good surface match. Has anyone discovered how to do this?

[sculptor]

first question
what resin?

second
was patch same ratio(resin, cat., bronze powders, thixative) as surface?

3rd
to what grit, did you sand it?

4th
same resin batch? & did the resin seem to behave the same way?

show pix?

i've been repairing repatinaing rebuilding some polyester and bronze powder sculptures for up to 30 years and was always able to recreate the finish i desired

when i want to "age" the bronze powders(read head for black)
i used acetone in the mix,
but not recomended as it is darned toxic, and deteriorates the resin faster than many years in the sun and rain and snow and birdshit

if you're trying to perfectly match the surface that matured in the mold, the solution is obvious
mastering the control of the materials is a craft unto it's own

show pix, and type details and I'll try'n walk you through it
cool?
rod

[Stevem]

I have applied bronze powder mixed with shellac. When it dried I polished it back to blend it in with the surrounding surface. You might give that a try.

Good luck,
Steve

[Santosh Yes]

http://www.photodump.com/direct/santoshaha/Graphic2.jpg Hi Sculptor, thanks very much for responding to my post. Below are two photos which give an indication about my problem.
1. The resin I am using is general purpose polyester resin which I bought at the hardware store (here in Lithuania) it's for fibreglass laminating so I assume it has no wax in it, it seems to work fine. The origional resin was General purpose polyester resin from Tiranti's in UK, ( I also have here some clear casting resin from Tiranti's UK). 2. The origional ratio was about 50/50 with a little more bronze (as was recommended), I tried a similar mix to repair but it want metallic enough and i noticed that the origional mix only appears metallic on the surface - sand off a fraction of a millimetre and it becomes dull brown, (seems as the bronze powder collects at the mold surface when it is rolled). Now I am trying a ratio of 1/1.5 resin to bronze as I think this should be the maximum density possible (also accounting for 7% volume shrinkage of the resin) but this needs a bit of acetone to thin it (I wear a respirator). Even this doesnt sand back looking as good as the origional. I'm sanding with 320 grit. Yesterday I tried putting a bit of thixo powder and enough acetone to paint on thin layers, stirring vigourously before each brush stroke, quicker results but still visibly imperfect. Hope you can help.

http://www.photodump.com/direct/santoshaha/Graphic1.jpg

[Santosh Yes]

Also thanks Steven, I shall try that shellac technique.
Interestingly I have gone over my calculations again and assuming all the bronze particles were spheres and stacked up like snooker balls, then for 100ml filler there would be 24ml of space to fill (between spheres of bronze). So as resin shrinks about 7% by volume you would need 25.8ml of resin/catalyst mix ... of course you'd need a few drops of acetone to mix it up. Such a mix could'nt shrink...

[sculptor]

nice work
show complete in new picture?

there are other thinners for polyester resin-one is the key chemical ---(can't remember it's name-will search)

i suspect that the acetone may be darkening the bronze powders

then yes particles migrate to the surface-----so maybe a gentle touchup on surface with jabbing rather than brushing motions

rod

[HappySculpting]

Nice sculpture/emotion being showed. Could we sneak a peak at the whole thing?

~Tamara

[Santosh Yes]

Thanks for the compliment Happy Sculpting but I wouldnt like to post any pics of the whole sculpture until I have finished repairing the surfaces - that will be in a few weeks so please be patient.
I have ordered some styrene and shall try that jabbing technique Rod. I thought also that since this is a surface finish - exposure to air might also be causing a bit of under cure as I am not using gelcoat (waxed resin).They say gelcoat is unsuitable with fillers but perhaps in this case, thinned with a bit of styrene it might make a great base for paint the bronze?

[Santosh Yes]

http://www.photodump.com/direct/santoshaha/fudge.jpg

This is a close up pic (about 1cm by 2cm). As you can see I am going backwards in my attempts to create a matching bronze surface. The original surface is top right. This time I'm using waxed resin to prevent surface tackiness and thinning with styrene .. the result is still very poor. Can anyone help? :eek:








http://www.photodump.com/direct/santoshaha/bronze(5).jpg

[sculptor]

Original surface is on right and repair is the smoother surface on left?

if so, the original seem a lot more brilliant

rule of thumb in mixing bronze powders with resin
the larger the particle size, the more brilliant
the smaller the particle size, the more subdued, subtle, less brilliant

so if i understand the definition of your photograph---
have you tried using a different particle size?
if not, may i recommend that

best of wishes,
rod

[HappySculpting]

I know your main question is on repairing the cold cast bronze but since I can't help with that question I though I'd post anyway and say what a touching, romantic scene this is. Can't wait to see the front and other angles. :)

~Tamara

[Santosh Yes]

:eek: sorry sorry mistake !
- the original surface is top left - the bronze powder used is the same

Oh! Happy Sculpting thanks v.much. :p

[Santosh Yes]

Well I still cant figure out how to make a good matching bronze surface on the bad areas of my cold casting, perhaps it's impossible. I cant seem to get a smooth metallic surface so the subtle details of the original look messy :eek:

[nep75]

Just a thought. It might have something to do with the original was pressed against the mold and the patch isn't. What if you patch and then stick it in the mold real quick? Maybe I'm just rambling. I don't know what else you could try though.. sorry!
~ N

[Santosh Yes]

thanks NEP75 .. that probably might work but the bad bits I need to fix are where two parts of the mould meet (and have slight registration errors) so it wont help me in this situation.
Now I am going to try as follows:-
1. paint on catalysed resin (the resin type includes wax to counter air contact under-cure tackiness) thinned with acetone ratio 1:1. (the acetone rapdily evapourates leaving a very thin layer of resin with no brush marks)
2. dust on bronze powder and leave to cure in warm dry place. then dust off remaining bronze with medium brush.
3. repeat a few times
4. carefully and very lightly sand with 350 - 600 grade wet and dry paper
5. gently burnish with small circular motion.
suggestions are welcomed

[antoine]

hi..........
I am Antoine farrugia a Maltese stone sculptor....
I am starting to divert my work on metal sculptures.I am using the lost wax method.I obtained a mould from my original sculpture using the plaster of Paris.From this I obtained a copy using wax and applied vents,risers etc.To obtain the final ceramic mould ,I used normal local clay but this was a total failure.The clay mould became all cracked throughout.
Please could you advise on which material you supply to replace the clay I was using.
As a beginner, I am casting my sculptors in lead,but I want to start casting bronze in the future.
Could you please help me to find the right binder,any link from where can i buy it?
Best regards
Antoine Farrugia.