Guide: copying a wooden ornament

Assess and repair the ornament

Assess the ornament and repair damage and unwanted irregularities. With this porous 15th-century wood carving, careful preparation is especially important.

Remove dust

Blow away dust and loose wood particles with compressed air. A clean, dust-free surface gives a sharp, detail-accurate mould.

Apply release paste with a cloth

With wooden models, no adhesion between the silicone and the wood may occur, and hardly any oil from the silicone may seep into the wood. That is why we first apply a release paste. The liquids evaporate from the paste and a releasing residue remains.

Apply the paste to the wooden surface as described. Use a cloth or sponge for the flat areas.

Apply release paste with a brush

Treat hard-to-reach and deep-lying areas with a brush so the entire surface gets an even layer of release paste.

Let the paste dry to a white, powdery residue. This residue protects the wood and is easy to remove later with water.

Pour the first silicone layer (without thickener)

Pour a quantity of Silicone C-20 A into the mixing container and add 2% Silicone C-20 B. Mix the components well with a spatula.

Pour the silicone onto the ornament in a thin stream and fill all deep and hard-to-reach areas. This first, thin layer captures the finest details.

Apply the second silicone layer (with Thixo C)

The second layer is the support layer: it builds the mould up to thickness and gives rigidity. Pour Silicone C-20 A into the container again and add 2% C-20 B. Mix well.

Now add 1% Thixo C and stir again thoroughly. Let the mixture rest for 2 minutes so the thickener can do its work.

Apply the thickened silicone with a brush or spatula. Do not trap air; treat detailed or deep areas by dabbing. Apply a layer about 0.5 cm thick.

Smooth the silicone

Smooth the top layer as evenly as possible with a spatula or brush. A soapy solution helps: dip your hands (with latex gloves) into it, then the silicone sticks less and you can smooth by hand.

Let everything rest for a day so the silicone fully cures.

Cut the triaxial fibreglass cloth

The silicone is fully cured after 24 hours. Now we make a support shell that holds the silicone mould in shape during casting.

Cut the triaxial fibreglass cloth into manageable strips that fit the model, for example strips 1 metre long and 20 cm wide, plus several pieces of 20 by 20 cm.

Mix acrylic resin for the support shell

Fill a roomy bucket with the calculated amount of Acrylic resin A component (liquid). Add the correct amount of Acrylic resin B component (powder) and start mixing immediately, preferably with a drill and mixing attachment, until you get an even mass without lumps.

Then add 1% Acrylic resin thickener Thix A (so 150 grams for a 15 kg mixture). Apply the acrylic resin around 5 mm thick over the entire silicone model.

Lay in the first layer of fibreglass cloth

Lay the triaxial fibreglass strips onto the still-wet acrylic resin and press them on gently. The acrylic resin must not yet begin to cure.

Use a wide brush to press the cloth down well and spread the acrylic resin evenly. Smooth the surface and apply a second and possibly third layer the same way. Then let the support shell dry for 24 hours.

Assemble the mould in the support shell

Once the support shell has cured, remove it from the silicone. Then carefully remove the silicone mould from the original ornament.

Place the silicone back into the support shell correctly without deforming it. Set everything level and fix the mould so it cannot shift or tip over.

Cast the acrylic resin final model

In a large bucket, mix the desired amount of acrylic resin as in step 7, but now without thickener: the resin must be poured as fluid as possible.

Pour at one spot and let the resin flow into the mould calmly, without splashing. This leaves few air bubbles. After pouring, tap against the mould so remaining air bubbles release and rise. Let the acrylic resin set for around 30 minutes.

Reinforce the final model with fibreglass

Mix a small amount of acrylic resin (around 1 to 2 kg) and spread it over the cast model. Apply fibreglass cloth and smooth it with a brush or by hand.

Repeat this 3 to 5 times for sufficient strength. Then let the model cure in the mould for 24 hours. Remove the model after 24 hours and let it cure and dehumidify for another 24 hours, on wooden slats if needed.