Timber Sculpture to Silicone Mould Form

For this instructable I wanted to make something unique and different that would be a challenge. Timber sculpture and working with timber is something I have always loved. There is something special and organic about timber work that I love. Maybe it's the feel of it or maybe it's the different grains and textures you can choose from. Working with silicone mould forms, however, is something I have never done before and wanted to give it a try.

I haven't made many Instructables lately because I have been pretty busy and two days before my birthday I had most of my tools stolen from my car so I'm excited to finally start posting again.

Now on to the instructable. I decided to make a sculpture as a prototype to then make a silicone mould form. I thought this would be a great opportunity to take everyone along for the ride. In this instructable you will learn how I glued, shaped and finished the sculpture to a finish that can be moulded, how to make a two-part mould and how to pour silicone.

When it comes to timber there are many to choose from.

What you want is a very hard timber. You want your project to last, be wear resistant and not chip, splinter or dent. The timber must also be properly seasoned and stable, free from knots and other imperfections. There is hours of sanding in a project like this and you wouldn't want all the work to go to waste. I would recommend the following for a lasting project.

For America;

Mahogany, Snakewood, desert ironwood, hickory, mesquite (high mineral content, destroys tools), Walnut, Maple (choose harder pieces), birch and Oak

For Australia:

Ironwood, bluegum, redgum, jarrah, ironwood, mulga, gidgee, acacia, etc

Timbers not to use would be soft timbers,Pines cedars and alike.

For this project I used a desert timber (Mulga) which is known for its hardness. The aboriginals often chose to use this for their boomerangs because of its hard use and ability to be sanded very smooth for aero-dynamics. For the sides I used New guinea rose wood for its beautiful appearance and workability.

Next you want to use a saw to dress your timber into usable pieces. Don't be too fussy on making the surfaces flat as you will not see most of them.

Then mix up some two part epoxy to glue your pieces together. I used 24 hour araldite.

Choose a strong clear adhesive. Use a generous amount of the glue between your layers of wood and allow 24 hours to dry. I put mine on a plastic bag to prevent the glue from sticking to the surface of the board I rested it on.

Sculptures that I think look best are the ones with smooth running lines. In nature there aren't many straight lines. There also isn't much symmetry and having an a-symmetric design draws the eye to focus points your work.

I used an orbital sander to flat sand one side to prepare it for gluing my design on.

I used a spray glue called Trim-tex. It is used by plasterers to stick external molds onto construction corners in houses. It works great for this application. Contact adhesive would also be suitable.

Use a scroll saw or band saw to cut out your shape. I left a little bit extra on right the way around.

My grandfather who was a cabinet maker used to say

"You can take timber off but you cannot put it back on"

Before the rough sand it's a good idea to round the whole outside of your cut out piece. Look at the job as a 'whole piece' - sand out any imperfections that disrupt the even natural flow of your piece. Once that was done I sanded the job to taper to one end leaving the ends un-sanded in this process.

Next I began sanding the shaft between the two ends using the belt sander. Start by making 45 degree sanding lines on all four corners of the job. Blend these in to a round but don't get carried away. Take your time.

Next use long strips of sanding paper to help you round the shaft. I clamped one end to the bench with a quick clamp. Grab both ends of the paper and pull down while alternating up and down with both hands. I used 80 grit paper which is quite course and rips the timber away pretty fast.

I used a Dremel with a sanding drum to add finer detail and round the two ends. Follow the same rule of stopping and looking at the whole job and make the necessary adjustments.

Work those ends to a nice look and round things off roughly to a 120 grit paper. At this point I gave it a quick spray with a clear coat. This prevents the lighter coloured timber from getting dirty while people handle it and also it preps the grain by semi sealing it. When your first coat is applied to any timber it lifts tiny pieces of grain upwards. If you want a smooth coat on anything this first coat is lightly sanded to "knock off" those tiny grain hairs.

I began sanding out all the uneven lines.

I took these photos to show how something can be shaped pretty accurately by eye. Hold your project so you can look down the shaft/head. You can see how there are uneven sanding problems here and there. Sand the first one you see to correct it and then tilt the shaft up a little. Work around the piece to sand all these out till you are satisfied.

Now use 120 grit to make everything uniform before swapping to a 600 grit wet and dry paper.

You can see how 600 grit really smooths everything and how the initial design has changed. Once sanded to 600 it will feel silky smooth. To give people an idea how smooth, if this was held gently it will slide in your hand. It now does not feel like rough timber but more like a smooth stone.

Now it's time to find any small holes, pits and other things that need filling. I used a paint brush to dust the whole thing and reveal any holes hiding under the dust. You could also use a compressor.

Next mix up some more epoxy and fill the big holes leaving a small amount of "overfill" on each hole. Once dry sand these back first with 120 grit then back to the 600 grit.

You will notice on the lighter colored timber there are small pits where the natural grain has grown. One way to overcome this is to use a water-based filler of the same color mix with water to make a slurry. Paint this on (only the light areas) and allow to dry. Use the 600 wet and dry to sand it lightly till you can see the timber. In my case I am going to just use lots of clear coats and sand in between each coat. I would advise filling the grain as this will save you HOURS of time.

There are a number of products on the market and much debate as to the correct - or more so, the safe - coatings to be used on timber sculptures and alike. I am unaware of a company that makes a product specifically for coating timber that is completely safe, but if you find one, post it in the comments.

One of the most common for hobbyists is a finish called "Salad bowl finish" It is a food grade coating for wood turners to use on salad bowls. My understanding is it is mostly a paraffin based product.

I am skeptical as to if this does provide an adequate seal on the timber but as always I encourage people to do their own research.

What I would recommend is a medical grade epoxy. This would fall into the Class 6 grade epoxy's suitable for intradermal use. They are used in hospitals and for surgical instruments and contain no harmful chemicals. Another name for this type of coating is medical grade co-polymer.

What I used on my project is a nitrocellulose coating that is approved by Australian standards for use on children's toys and in nurseries. It contains no harmful chemicals and once dry is safe to use for whatever you want.

Keep spraying and sanding with 600 in between coats to achieve a smooth waterproof coating. You will see the small pits start to vanish till it's completely smooth. The end result is well worth the time. You can see every detail in the timber as the sunlight hits it and it shimmers as you move it.

Now you can give it to a friend or put your sculpture on display in a public place.

I wont go into too much detail as there are lots of tutorials for making a two-part mould already. I thought the process I chose might be of interest to some people out there. Two part moulds are great for replicating objects with very accurate results. They are expensive to make and time consuming but in the long run very helpful if you want to make repeats of any shape.

First up , put down some modelling clay and sit your object on it, then build up the clay around it.

Next, smooth out the clay where it meets your object. I used a glaziers silicone screed.

Clean any clay off the object and add a pouring funnel made from clay.

Use a blunt object to make small holes in the clay right around your object to act as a key to lock the two halves together so it won't move when you're pouring.

Follow this by making a vent hole at the opposite end of your object so any air bubbles from the final pour will escape. Bring this to the top of the mould near the funnel you will pour into.

Use something smooth to make your box from. I used perspex and hot melt glue so i could pull the mould apart.

Next, mix up your mould media. I used Pinkysil which I found to be a great casting silicone. Easy to measure quantities and work with.

Once mixed, spray "mould release" generously on your clay and object.

Once your silicone is poured use a hair dryer to take out any bubbles. Repeat this till no more bubbles surface.

Leave this to dry for the correct amount of time suggested on your product box.

Next cut away the mould sides and remove the clay. Except for the funnel and vent clay.

Be very very careful when performing this step! You do not want to "move" your object on the silicone side at all. Doing so will leave you with a bad mould.

Clean what was the clay side of your object carefully and re-glue the sides of your box again.

Re-spray mould release. Repeat pour step.

After drying, take the sides of the box down again and use a razor knife to carefully separate the mould.

Clean your mould out with warm soapy water and leave to dry. Once dry, spray mold release on both halves. Hold the two halves together with plastic wrap and pour your silicone in. Bump mould gently to remove bubbles and leave longer than recommended to cure.

After it has cured, open the mold and trim any over-spill with a razor knife and cut off the vent and funnel holes.

Your finished product should be very close to the master object! Check it out, wave it around, put the master and mould form on display side by side as a tow-part piece and be happy cause... You made it!!!!