The aim of this project has been to provide quality reflective coatings to astronomers. This may sound like a strange thing for us to do at Fieldview, but this is not the case.
Simon is a solid state physicist, and has spent a number of years coating aluminium onto glass and delicate organic electrical devices in a research environment. Coupled with his chemistry and specialist materials background he is well qualified to research into and offer quality coatings.
We are indebted to the Norwich Astronomical society and David Jackson for support and the donation of vacuum coating equipment.
Glow discharge cleaning of mirrors
An 8inch mirror reflecting Simon taking a picture of it, Smile Please
Mirrors coated up to 10 inchs (250mm) in diameter.
We are now at the stage of long term testing, the coatings are great, but how long do they last for ? So if you want to join in and get your mirror coated at the bargain price of then get in touch with us. All we ask is that you let us know how the mirror performs.
During this testing period the prices for coatings are :-
£20, for primary mirrors and £5.00 for flats.
You can phone on 01328 820083
for gold top coating add £5.00
For the future
We are preparing to build a coating machine that will coat mirrors, firstly of 18.5 inches (462mm) and then 20+ inch(500mm) mirrors, we hope this service will be introduced over the next couple of years.
At first we are offering simple Aluminium coatings, however we will be developing new top coatings to enhance the lifetime of the aluminium.
UPDATE (15/05/03) see below for Gold Overcoating
10 inch(250mm), 8 inch(200mm) and 6 inch (150mm) mirrors coated at Fieldview.
Secondary Mirror - Overcoated with Gold
Opposite is the secondary mirror from fieldview's 14.5inch Dosonian Reflector.
We have just re-coated this mirror because on examination it was clear that the original coating had been poorly applied. Approximately 1/3 of the surface was bubbled, this indicates that chemicals used for cleaning the glass had not properly been removed, the mirror finish had probably become like this very shortly after it was coated.
This mirror is now coated with Aluminium and then overcoated with a thin layer of Gold.
GOLD OVERCOATING. - only £5.00 extra.
We are all looking for that coating to give the best reflectivity that has a long lifetime, over the years Aluminium has become the standard, however aluminium oxidises , initial that forms a protective aluminium oxide layer on the mirror surface, this affords some protection.
Mirrors are also coated commonly with silicon oxide to protect them. However we are investigating GOLD as an overcoat. This idea comes from the electronics industry, where gold it commonly coated onto aluminium. Unlike silicon oxide gold is a reflective coating, gold is also inert, and is known to give good coatings on aluminium.
We only apply a thin layer of gold, Our initial results seem to show that the coating is brighter than aluminium alone (but at this stage it is a subjective observation) . This is not really surprising, normally as soon as the aluminium is exposed to the atmosphere the surface starts to oxidise and the mirror starts to lose some of it's reflectivity. But with the thin gold layer oxygen is prevented from reaching the aluminium surface.
The big test for this coating will be to see how long lived they are. Theoretically they should last a great deal longer than aluminium alone, but this is what we will now put to the test!
If you want your mirror over coated with gold then add £5.00.
This is a theoretical graph of reflectance of a gold overcoat compared to that of a fresh Aluminium coat that has not suffered any exposure to atmosphere and thus coated with the protective oxygen layer. The lower trace is the gold coating, as you can see their is little difference, however over time the aluminium only reflectivity will drop as the top surface oxidises.