How to Coat a Telescope Mirror Yourself | Telescope Mirror Coating DIY

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Telescope Mirror Coating DIY

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Steps for Telescope Mirror Coating

  • Step 1: Strip the old coating
  • Step 2: Prepare the praying chemical mixture
  • Step 3: Clean the mirror
  • Step 4: Sensitize the mirror surface
  • Step 5: Spray the mirror surface with the silvering mixture
  • Step 6: Apply anti-tarnish coating and let dry

Did you know you can coat a telescope mirror yourself using store-bought equipment and chemicals? In this post, I will give you a step-by-step guide on how to silver-coat your telescope mirror.

Let’s get started!

What You’ll Need for Telescope Mirror Coating DIY

You will need the following to get started:

A spray kit

It has the chemicals you need and the sprayers. You can buy this online from stores like Angel Gilding or from your local mirror stores.

Most kits come with everything you need, but you may want to check and ask what you need to get.

You also choose to buy the chemicals only and make your own sprayers. If you choose to do this, make sure that the sprayers are compatible with your telescope mirror.

A one-gallon yard sprayer

You will spray the mirror with water when rinsing. There is going to be a lot of rinsing, so this sprayer will be effective.

Personal protective equipment

You will need to get goggles, a mask, and gloves. Make sure that you wear protective clothing as well, like long sleeves and pants, to protect your skin from chemicals.

Ferric Chloride and Baking Powder

Most telescope mirrors are coated with aluminum by manufacturers. You will need the Ferric Chloride to strip the aluminum acting and the baking powder to neutralize the Ferric Chloride.

Precipitated Calcium Carbonate

You can easily buy this online. You will need it to clean the bare mirror once you have removed the old aluminum coating.

A lot of water (distilled)

For a 28-inch mirror, for instance, you want to have like eight gallons of distilled water. As I mentioned before, there is going to be a lot of rinsing.

A plastic tub

This should be larger than the mirror you are going t in silver-coat. It is going to catch the water when you are rinsing the mirror.

A spraying jig

You will need this to hold and tilt the mirror as needed when you are spraying it. You can buy this from your local mirror store.

Preparation for Telescope Mirror Coating

It is important to calibrate the sprayers. This way, you’ll know they’re applying the same amount of chemicals.

Fill your sprayers equally with distilled water and spray them for the same length of time before doing anything else. Be sure the sprayers are empty at the same time. Adjust the nozzles accordingly if they don’t.

Step 1: Strip The Old Coating

This is where you will need the Ferric Chloride and the Baking Powder. Cover the mirror with some paper towels, then pour the Ferric Chloride evenly in the paper towels.

The chemical will soak the paper towels and spread them all over the mirror.

Ferric Chloride dissolves aluminum while leaving the mirror. If the mirror was coated with unenhanced aluminum, it should be dissolved in about two hours.

It might take longer if the aluminum was enhanced. It is therefore advisable to do this step in the evening and let it soak overnight.

Remove the paper towels and rinse the mirror with distilled water letting the water run into the plastic tub you placed under the jig. The mirror should be bare at this point. Dissolve any aluminum coatings with cotton balls soaked in ferric chloride and rinse accordingly.

Once the mirror is 100% clean, pour baking powder and rinse accordingly with distilled water.

Step 2: Preparing the Chemical Mixture

Mixing the chemicals is easy. Carefully follow the procedure for mixing the chemicals provided by the manufacturer. You want to follow the instructions carefully so that you can achieve a smooth coating.

A simple mistake can lead to a waste of money and time.

The number of chemicals you mix will depend on your mirror size. Again, all the guidelines as to what amount to mix are always provided by the manufacturer.

Step 3: Cleaning

This is a critical part of the entire process. At this point, you only want to touch the mirror with gloved hands, so you don’t introduce any dirt or oil onto the mirror surface.

Tilt the jig into a horizontal position and sprinkle the precipitated calcium carbonate onto the mirror. Use two or three cotton balls held together in one hand to spread the chemical on the glass surface.

You can spritz some distilled water to achieve the proper water consistency as needed.

Starting from the side of the mirror, scrub the mirror in circular paths. Add more precipitated calcium carbonate as needed.

Once all the mirror surface is done, tilt it back to about 30 degrees and rinse with water.

Step 4: Sensitizing

The sensitizer was mixed up at the beginning of the process, so it’s ready. Put on your respirator and safety glasses, swish the spray bottle to ensure that the sensitizer is fully mixed, and then spritz the mirror’s surface as evenly as possible.

Wait for about 30 seconds. Tilt the jig to 30 degrees, then rinse the mirror with distilled water. 

Step 5: Spraying

Swish the reducer and silver solution bottles gently to ensure that they’re thoroughly combined. You should still have your protective gear on.

Make a tiny test spray in the plastic tub to ensure that they are properly spraying.

Hold the bottles about 18 inches away from the surface of the mirror. Spray for approximately five seconds, then stop and look at the mirror.

It will become splotchy grey. After ten more seconds of spraying, you’ll notice an incredibly bright and gleaming silver coating start to develop.

Spray at most two more bursts of five seconds, so the entire mirror is evenly coated. Put the bottles down carefully and rinse the now silver-coated mirror with distilled water.

Step 6: Applying Anti-Tarnish Coat and Drying

Here, you will need to follow the steps provided by the manufacturer of the chemicals on how to apply the anti-tarnish solution. It is a simple procedure and should only take a few minutes.

Once you rinse off the anti-tarnish solution with distilled water, use an electric or handheld hair dryer to dry the water droplets on the mirror.

Final Thoughts

Coating a telescope mirror is no easy task. It requires patience, meticulousness, and knowledge.

If you’re not careful, it’s easy to make mistakes that will require additional time and money for cleaning or polishing. Hopefully, this article has been helpful to you, and now you can easily do the coating yourself.

If you would like to take a look at more advanced stuff you can do, check out our article on How to Grind a Telescope Mirror.


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