Posted by Alumilite on Sep 3rd 2021


I need new tail lights but have no equipment!

We are going to take a look at the process for casting clear lenses without the use of equipment. This
process will walk you through each and every step.

Products Used


Step 1 Warm your mold

The first step to casting your tail light lens is to warm your mold to help the resin cure properly in thinner sections. We recommend 15-30 minutes at 150 F or 1 minute per pound of rubber on high in a microwave. This will make the molds warm to the touch but should not be so warm that you can not hold onto them.

Step 2 Alumilite Water Clear

Next open up your Alumilite Water Clear kit. Products used in this how to are below and above.

Step 3 Measure equal amounts

Measure equal amounts of A and B. Shown in this picture is an inexpensive digital kitchen scale Alumilite
sells that is perfect for measuring silicone rubber and resin.

Step 4 Add a few small drops of dye

After you measure out the A side, add a few small drops of dye to color the resin. Here we will add a few extra drops or red to help differentiate resin in the pictures.

Step 5 Add as much as you would like to see

The best way to consistently color every casting is to add the dye to the A side container. If you don't want to color all of your Water Clear, count the drops you add to the A side and repeat this same number for every cast piece you pour. The more dye you add, the darker the color. What you see is what you will get so only add as much as you would like to see in your finished part.

Step 6 Now add the same amount of B side

Now add the same amount of B side as you did A side. This will keep you on proper 1:1 mix ratio by weight.

Step 7 Stirring time!

Put your stir stick down to the bottom of the container and stir the resin extremely slow for 2 minutes. This will drastically reduce the amount of air bubbles you create as you mix seeing as though we will not be using equipment to help us eliminate bubbles in our casting.

Step 8 Start pouring

Start by pouring some of the resin down the side of the mold very slowly. Fill the mold up approximately 1/2 way.

Step 9 Paint resin onto the male portion

Next, paint the remaining resin onto the male portion of the rubber mold. This will reduce the surface tension from that half of the mold and help the air bubbles migrate to the seam line and out of the casting.

Step 10 Line up the locators and on an angle

After you've painted some resin on the male half of the mold, line up the locators and, on an angle, slowly lay the male half onto the female. This will allow the air to be squished out the seam and reduce the amount of air that will be trapped.

Step 11 Lay the top half on the bottom

Simply lay the top half on the bottom and do not push it down. Make sure the locators and mold are in the proper place. Then walk away from it. Let the mold sit for a minimum of 2 hours. If your part is thinner than 1/8", it is recommended to post cure the part in an oven at 150 F for 30-60 minutes to help the thin resin piece to cure properly. Allow the mold to cool before demolding.

Step 12 Separate the two halves

Once the resin has cured, separate the two halves of the rubber mold.

Step 13 Flash around the part

Here you can see the lens with flash around the part still sitting in the female half of the mold.

Step 14 Peel the flash

It is often times easier to remove the flash while the part is still in the mold. Simply peel it away from the
seam line and throw it away.

Step 15 Or trim the flash

The other option is to simply pull the part out of the mold and trim it off with an Exacto knife.


Finished Project

Here you can see the original lens (left), along with the two piece rubber mold (top), and the darker cast reproduction (right). As you can see our cast replica is darker than the original. If you wish to match an exact color, simply run small test batches to figure out the exact amount of dye you need to match the color you desire. Then cast your piece with that amount of dye added to the Water Clear.