Experimental Shell Forming Technique

[Gil]

The development of a new modeling paste (my own formulation) that will work with paper has been burning a hole in my creative processes as of late. I had to test it on something other than as a filler to determine whether it's suitable for advanced modeling techniques to satisfy my curiosity...,

A simple ovoid shell was designed and printed on chipboard (think low profile tank turret here). The piece was cutout and worked with burnishing tools on soft block printing pads to curl the leaves together. Nylon tulle (bridal veil material), used to reinforce the assembly, was wrapped around the periphery closing the petals together. Modeling paste was worked into the tulle adhering it tightly to the chipboard surface. A top layer of tulle and paste was added to the periphery and to the top at which point the assembly was set aside to dry. The whole process is very similar to fiberglass and resin layup methods but has the advantages of water cleanup and zero fumes.

The sanding and fill process yielded the finished test shell below.

The modeling paste passed all my critical requirement points:

- Very low moisture transfer to the paper
- Very good workability
- Sands and carves like wood to a polished surface
- Strong and impact resistant
- Water resistant
- Bonds easily to itself
- Has adequate working time
- Quick drying
- Consistency can be varied from a mortar mud to a casting cream

+Gil

http://img149.imageshack.us/img149/949/experimentalshellxh3.jpg

[whulsey]

Looks really interesting, will be following your expriment. Have done similar with plastic using MEK or Testor's liquid cement, but fumes will just about knock you out (literally).

[Leif Ohlsson]

Right now I'm thinking WWI rotary engine cowlings. I hate the petal version, and don't like the segmented rings very much either. Something is needed to smear onto the segments, which then can be sanded down and painted, preferable with gouache or other water soluble colours. You seem to have hit it right on. Leif

[Gil]

Hi Leif,

Cowl rings are a natural application for modeling paste.

There are several problems that factor into the reasons motivating the development of this method. The first is that I've been using thin strips of masking tape to hold the sections together while spreading PVA glue on the inside. The strips must then be warmed before removing else the tape will tear the surface. The outer seams then need to be "filled" in with glue and set aside to dry. The outside surface then needs to be filled and sanded smooth. The thought that taping, gluing and filling could be easily carried out with modeling paste and nylon tulle. The only question being, would the nylon tulle sand as easily as the dried modeling paste? Luckily, all the right factors came together providing just the right solution. The solution is similar to fiberglass and polyester resin layup.

Another area I want to explore in the future is the ability to apply aluminum foil for a natural aluminum finish. I've also noticed that some of the advanced modelers are sanding the underframe down and splitting the surface paper or using thinner presentation paper in an effort to achieve compound curved surfaces. This is much easier if the internal structure is stiff enough so that the surface paper can be burnished down. Sealing the surface of the presentation paper with acrylic coatings allows it to be burnished. Covering the surface of the underframe with modeling paste allows it to be sanded and still remain "hard" enough to have the surface paper burnished on.

So the modeling paste is just one part of what has turned out to be a very long term project...,

+Gil

[Leif Ohlsson]

Gil, what is modeling paste actually? - Leif

[B-Manic]

Gil, what is modeling paste actually? - Leif

What Leif said. What is it, without revealing any trade secrets of course :)

[lee4752]

Try Elmer's wood filler putty. It thins and cleans up with water and has no fumes.

[Gil]

Modeling paste is simply a medium with a filler. In the case of acrylic modeling paste you can use an acrylic paint with whiting (calcium carbonate-marble dust). Additives give the paste working abilities which are key to satisfying the modelers needs.

The mixture that's been developed can be made thin to use as a crack filling glue without compromising the structural qualities of the paper or made thick to build structural shapes overlaying the paper without crushing the paper structure. Drying time can be accelerated by heating with no adverse effects (15-20 minutes on the radiator).

The follwing is from Liquitex - Products: Mediums: Modeling Paste (http://www.liquitex.com/Products/gelmedmodelingpaste.cfm:)
It gives a good account of the available commercial product:

http://www.liquitex.com/imagestopnav/topnav.png Paints (http://www.liquitex.com/Products/paints.cfm) Mediums (http://www.liquitex.com/Products/mediums.cfm) Varnishes (http://www.liquitex.com/Products/varnishes.cfm) Additives (http://www.liquitex.com/Products/additives.cfm) Surface preparation (http://www.liquitex.com/Products/surfaceprep.cfm) Software (http://www.liquitex.com/Products/software.cfm) Retailers (http://www.liquitex.com/Products/retailers.cfm)


http://www.liquitex.com/Products/images/mediums/modelingpaste.jpghttp://www.liquitex.com/Products/images/mediums/gel/modelingpastetitle2.jpg
Attributes



Extra Heavy Body and very opaque.
A marble paste made of marble dust and 100% polymer emulsion.
Used to build heavy textures on rigid supports and create three-dimensional forms.
Dries to the hardness of stone. It can be sanded or carved when thoroughly dry.
Can be handled like clay if the top of the container is removed and some of the water is allowed to slowly evaporate until it reaches a clay-like consistency.
Adheres to any non-oily, absorbent surface.
Drying too quickly causes mud cracking that is usually cosmetic, not structural.
When mixed with acrylic colors will act as a weak tinting white, while increasing thickness and rigidity.
Excellent substrate for acrylic paint, oil paint, oil pastel, oil bars, watercolor, graphite or dry pastel.


http://www.liquitex.com/Products/images/mediums/gel/model_paste_info2.jpgDirections



Apply with knife, brush, cake decorating tools, etc.
To prevent shrinkage cracks (mud cracking), dry slowly by covering loosely with plastic wrap. Apply less than 1/4" thick.
Mix with acrylic colors to produce a colored tinted paste.
When dry, Acrylic Modeling Paste may be painted with acrylic or oil colors.


Application



Sculptural: Apply in thin layers allowing each layer to dry before applying next layer. If cracks appear, allow to dry and fill in with additional thin layer of Acrylic Modeling Paste.
Rigid support: Use straight from container.
Flexible support: Mix Acrylic Modeling Paste 50/50 with Gloss Gel Medium, Matte Gel Medium, Gloss Heavy Gel Medium, or Super Heavy Gel Medium.
Ground: Apply a thin layer of Acrylic Modeling Paste to rigid surface (i.e. wood), using a palette knife, trowel or roller. Let dry, then sand smooth. Repeat if necessary.
Absorbent ground: Mix 1 part Acrylic Modeling Paste with 3 parts Liquitex® Acrylic Gesso. Apply with trowel or roller. Let dry, then sand smooth. Repeat if necessary.
Paper-Maché: Mix Acrylic Modeling Paste 50/50 with Liquitex Gloss Gel Medium, Matte Gel Medium or Gloss Heavy Gel Medium. Soak paper in this mixture.



I've been using the Liquitex product for several years. It holds up to the manufacturers claims but falls short of fully satisfying my needs for card modeling. I guess the one complaint above all others is that it takes too long to cure to the point where it can be sanded and/or carved. And even then the surface does not sand as well as I would like (on the gummy side). The pot life is good but the cure time is just too long (> 24 hours in some cases). Another sticking point is cost, Liquitex is too expensive. Dick Blick offers a modeling paste at a much lower cost but I haven't tried it (Blick Artists' Acrylic Modeling Paste - BLICK art materials (http://www.dickblick.com/zz006/23e/)).

The last application issue involves thinning and thickening of the paste. When thinned with water it has a tendency to wet the paper surface causing the paper to lose its structural rigidity resulting in general failure and frustration on the modelers part. It becomes too thick when water is allowed to evaporate overpowering more delicate paper structures.

I've actually been pounding on the surface of the shell with a nylon headed hammer using it as a forming buck. It's held up to this outlandish punishment without complaint..., This is what I call Tuff...,

+Gil

[whulsey]

Doh...and a slap up the side of the head. I've used this stuff for years in art work along with different gel mediums, hadn't even thought about using it on a model. And yes, like all acrylic art products I've worked with it tends to be a bit rubbery to sand.

[scyg]

Gil - your first post made it sound like you've developed your own formula. Could you share that with us, or are you waiting to patent it first?

[redhorse]

Doh...and a slap up the side of the head. I've used this stuff for years in art work along with different gel mediums, hadn't even thought about using it on a model. And yes, like all acrylic art products I've worked with it tends to be a bit rubbery to sand.

Yup, me too. Duh.

I really don't like sanding this stuff at all though. Hmm, I'm now wondering what Magic-Sculpt would be like. Maybe too brittle, but water soluble before curing and it sands really well. Plus it cures faster under a light bulb.

[Gil]

Good question Simon.

I'm fairly convinced that the mixture does have a place in the modeling and art community. I would categorize it as a hard gesso but with a much greater modulus of elasticity and is resistant to cracking. The resulting material is amazingly stable.

Some preliminary Patent searches indicate that the mixture is a form of ordinary joint compound or in short "Spackle". The major difference is the respective percentages of binder, filler and thickener.

The intellectual property coverage is fairly complete so there's not much sense in filing a Patent. It is, however, a proprietary mixture which translates to trade secret but this could easily be found out by a diligent review of the material.

So should I go into the "Tuff Stuff Smoothing Cream for Cardmodels" or let everyone in on the formulation...,

Like I really have to ask...,

+Gil

[papermodelfan]

Just to clarify. In the post at the top, where you developed the turret shape, did you then put the tulle and paste on the outside of the shape? I guess so, as that would let you sand it to a smooth round shape. Seems like the method could be used for radar domes, underwater nose bulbs, and many smooth rounded aircraft parts? Rob Tauxe

[Gil]

Hi Papermodelfan,

Correct. The tulle is used like a piece of stretchy tape to bind the panels together. The paste tacks the tape to the surface. Two or three layers are nearly indestructible.

+Gil