Getting even seams on a two-part mold?

[Birdie]

No matter how hard I try, I always seem to have problems getting the clay really flat where it meets the pattern, leading to pitted/deeper seams when the resin is poured.

Has anyone got any tips or tricks when making the mold for getting a nice, even, and minimal seam-line?

 

[jackdoud]

Try using more registration points.

 

[Birdie]

To illustrate, I seem to end up with this:

Instead of this:

When I try to level the clay 'drag' around the pattern and mouldbox, I tend to end up with dips instead :unsure

 

[LeMarchand]

When i do a 2 part mold, the last thing i do is build the box around it, this leaves you space to work the clay around the model. Long toothpick (the pointed end work great to level the clay around it by carefully scraping the clay around the piece you are molding.

When you are happy, put the box around it and use a round piece of wood and push the clay against the walls.

hope i make sense

 

[clonesix]

Sorry, but your pics are filtered, and I can't see them. So I hope this answers you question. Otherwise I will have to wait until I get home to understand the problem.

The best parting lines are cut with a good rake. It really depends on the difficulty of the pattern.

 

[exoray]

Although wasteful, I have found for me the best way to get the clean seam line (assuming it's a straight parting line and not wavy or contoured) is to apply the clay bed but no all the way up to the part line, model the clay just bellow it... Now the sneaky secret I use, get some silicone thinner, and mix up a very small batch of silicone with say 10%-20% thinner added, this will make it pour, degas and self level much more readily... You are not really worried about the integrity of the thinned down silicone you are basically just using Mother Nature to create a level surface bed

Anyway with the mold on a level surface (I keep some shims handy just in case it needs some adjustment) pour this super thinned out silicone into the mold, just a skim coating of it over the existing clay bed bringing you up to the part line... Let it cure until firm, you don't really have to wait until it's fully cured, spray on some release and then pour that side... When you flip it over and pull out the clay, simply remove the thin sheet of silicone from that initial pour and you have a SMOOTH finish and clean parting line...

And if you are like me that HATES cleaning clay off the master and doesn't care about wasting a little more silicone you can just clay up close to the part and use the same technique of letting the initial skim coat silicone fill in the void...

For me personally the few dollars or so of wasted silicone is well worth the cost in labor savings and frustration...

 

[fettster]

i use a oil paint pallet knife to flatten my mould wall

 

[Birdie]

Although wasteful, I have found for me the best way to get the clean seam line (assuming it's a straight parting line and not wavy or contoured) is to apply the clay bed but no all the way up to the part line, model the clay just bellow it... Now the sneaky secret I use, get some silicone thinner, and mix up a very small batch of silicone with say 10%-20% thinner added, this will make it pour, degas and self level much more readily... You are not really worried about the integrity of the thinned down silicone you are basically just using Mother Nature to create a level surface bed

Anyway with the mold on a level surface (I keep some shims handy just in case it needs some adjustment) pour this super thinned out silicone into the mold, just a skim coating of it over the existing clay bed bringing you up to the part line... Let it cure until firm, you don't really have to wait until it's fully cured, spray on some release and then pour that side... When you flip it over and pull out the clay, simply remove the thin sheet of silicone from that initial pour and you have a SMOOTH finish and clean parting line...

And if you are like me that HATES cleaning clay off the master and doesn't care about wasting a little more silicone you can just clay up close to the part and use the same technique of letting the initial skim coat silicone fill in the void...

For me personally the few dollars or so of wasted silicone is well worth the cost in labor savings and frustration...

I love this idea :love

What do are you using for the 'male' registration, small bolts or something similar?

 

[exoray]

I love this idea :love

What do are you using for the 'male' registration, small bolts or something similar?

Well this is likely to really get lost in the translation over the big pond but I use what they call 'beaded screen moulding' and now that you are lost I'll link you to some pictures that are likely worth 1000 words...

http://www.trimbytim.com/profiles/Shelf_Screen.pdf

And

It's a wood trim moulding that is used to secure screens to wood doors and such the old way before the rubber hose and channel method they use now... Being trim grade wood it's very soft and knot free so I seperate the individual beads with a razor and end up with lengths of domed profile wood, cut to length roll the edges over and you get long registration tracks to lay along side the part... Flip a few short lengths perpedicular to the main runs and you get some pretty good registration of the mold halves...

Since its only 1/4" tall many times I actually float it right on top of the skim coat of silicone rather then anchor it down...

 

[brashsculptor]

Exoray, you have just saved me a ridiculous amount of time!! I love that trick!

 

[Tearawayface]

Here a slide show of the making of a mold. At 2:42 (ish) you can see how I achieve what your trying to do. It may not make sense, but I'll try to dig up some better pictures. (it may take a bit... off to work right now)
I use water based clay for the wall. The oil based clay of the sculpt has been sealed and the detail is not harmed in the process. I use a flat tool to keep the wall perpendicular to the sculpt. you have to get as close to the sculpt without damaging it. Then I use a wet brush to,more or less, dissolve the residual clay against the sculpt and clean that up with a sharp wedge shaped sponge.
If you use a clay cutting guide to cut your slabs of clay, it does a lot of the work for you.
More to follow...

YouTube - Molding Yoda's Head & Ears

 

[Garthok]

exoray that is probably the best tip I have heard on here, thanks, I will be doing that from now on...brilliant!

 

[zenix]

...It's a wood trim moulding ...

any way you can take some pictures next time you do it, and post the pictures? or show us a picture of the process? My friend wants to see exactly how it looks

 

[exoray]

any way you can take some pictures next time you do it, and post the pictures? or show us a picture of the process? My friend wants to see exactly how it looks

Wow, nearly a year later and I finally see this reply... Yeah I guess I could take some pics next time on the process, might even just cast something for the heck of it for tutorial... I'll see how my time goes, I need to make some molds this weekend anyway so I will have everything lined up...

 

[robstyle]

Late too the game but ditch the clay and use a split board. Ive watched people spend more time trying to smooth clay than it takes to simply trace the outline of the item onto a thin piece of MDF, cut that shape out, fit the part to the hole and clay in around the opening.

Here is a super quick mold I had to do some time ago. For scale, thats a near 24" tip to end knife. I cheated the blade a little high to give thickness to it which is why you see clay over the edges. It also makes one side deeper so I can prefill and add an armature.

 

[Volpin]

ditch the clay and use a split board. Ive watched people spend more time trying to smooth clay than it takes to simply trace the outline of the item onto a thin piece of MDF, cut that shape out, fit the part to the hole and clay in around the opening.

I've also used foamcore for this same method, but with a brush-on mold.

 

[kwalsh0000]

Bit of a ressurection of this thread!

Am going to try this method tonight and attempted to thin the silicone with acetone (nail varnish remover ) to thin it out enough to flow like water but it didnt work.

Just wondering what the best way to thin the silicone is and does it flow like water? The piece is fairly long so needs to flow fairly well

Cheers!

 

[Finhead]

Bit of a ressurection of this thread!

Am going to try this method tonight and attempted to thin the silicone with acetone (nail varnish remover ) to thin it out enough to flow like water but it didnt work.

Just wondering what the best way to thin the silicone is and does it flow like water? The piece is fairly long so needs to flow fairly well

Cheers!

Depends on the brand your using. Smoothon makes a thinner for silicone, it works very well but it makes the silicone weaker the more you use and will take longer to dry the more you add.

 

[kwalsh0000]

Its just standard RTV silicone (no fancy name). Not too concerned about strength as its going to be used as above for the first thin layer then the proper silicone over that

 

[fettster]

Bit of a ressurection of this thread!

Am going to try this method tonight and attempted to thin the silicone with acetone (nail varnish remover ) to thin it out enough to flow like water but it didnt work.

Just wondering what the best way to thin the silicone is and does it flow like water? The piece is fairly long so needs to flow fairly well

Cheers!

Acetone won't work mate, you need to use White spirit but it will make the silicone softer and will shrink over time as the White spirit evaporates.