Mirror Recoating

You will find a recoating price guide and and an A4 Printable PDF Form to return with your mirror(s) at the bottom of this page.

One of the most important and very widely used services we offer is the re-coating of established or, coating of newly made mirrors. This service we offer is taken up from every corner of the globe as it offers both added reflectance qualities to mirrors, over and above what most other companies can offer and, a vastly extended lifespan of the reflective surface if care is exercised in looking after the coating.

For this service we offer Hilux as standard as it is so widely accepted in all astronomical circles as being one the best if not the best system available anywhere using aluminium as the reflective component of the optical stack. Stack is the technical term used to describe the multi layers of dioxides etc and the aluminium which are applied under vacuum to the mirror’s surface to produce a high quality reflective coating.

Some important points to consider when shipping a mirror(s) to us for re-coating.

Mirrors can be sent to us for re-coating whilst still attached to their adaptors/mounting plates etc. Because of the nature of the equipment used in coating a mirror we have to remove these parts for two reasons:

1. Many materials, especially glues, resins and some plastics, release volatiles and gasses which are constituent components of the adhesive/material. These gasses are detrimental to both the performance of the coating process and, the coating materials used in the coating process, including the diffusion pump oil, polyphenyl ether, which currently (2013) costs almost £1,000 a litre and the diffusion pump’s oil capacity is 2.6 litres.
2. To remove the old coating of a customers mirror we immerse the mirror into a bath of strong alkaline and inhibitor chemicals. Essentially these chemicals destroy the old coating and also, virtually anything else attached to the mirror. However, some mirrors have a sub coating which is compromised of mainly metallic oxides and termed dielectric. This coating cannot be removed chemically as the materials used are non reactive to even the strongest known acids. When mirrors are sent to us it is not always possible to detect this as the subcoating appears very similar to the top, reflective coating. In cases like this, we can and do remove the top reflective coating but are forced to re-coat over the sub, dielectric coating as it cannot be removed. If, over several years, the original subcoating can become etched with atmospheric pollution and damp, this may, on occasion, damage this sub coating and that can leave a final re-coated surface with this damaged ‘patter’ visible as a slightly duller section(s). We take every effort to try and identify if this is going to be a problem and in cases where we are fairly sure this is the case, we advise customers.

These are the two main reasons we have to remove everything attached, even a thin layer of glue or silicone rubber can ruin the process and damage the oil.

If you are able to remove all attached parts and any residual glues, paints, resins etc, we can then immerse the mirror in the ‘stripping solution’. If you are unable to remove these ‘attachments’ and adhesives etc, we can do it for you. It is not possible in the space allowed here to look at all alternative and options of these attachments and resins etc which we have to initially mechanically remove then use several different solvents to remove the enormous number of adhesive variants. If an optic is required to be centrally re-spotted there is a charge of £10 for this.

We can also, if so requested, re-mount your mirror(s) on their supports/attachments for you. Because of the hundreds of combinations it is not possible to display all these alternatives so, if you do wish us to carry out this function, please tick the box shown on the table and include a printed version when you send in your mirror(s) and we will contact you with details of costs involved.

We take the best possible care when coating a customers mirror and on arrival in our coating lab we carry out a thorough check of the mirror(s) you have sent us. We look for many aspects of the mirror’s condition and also whether there may be a problem with the newly coated surface we apply.

Some mirrors we receive have been kept is wet conditions or conditions where moisture occasionally condenses on the optical surface and stays for hours, sometime days. This is one of the biggest problems which cause degradation of the reflecting surface. The moisture gradually seeks out microscopic pin holes in the top protective layer of a mirror’s coatings and begins, ever so slowly, to attack the aluminium underneath this layer. Over the years, this action can also attack the glass but to a far lesser extent. However, glass needs very little attack to loose a little of it’s polished finish.

Unfortunately, there are one or two cases a year when there is very little sign of any attack on the mirror’s surface and we consider that it will coat to a virtually perfect reflecting mirror. The problem is that when coated, we come across areas which are slightly duller which, were impossible to detect in it’s original condition or when the old coating was stripped off. Let me stress, this is a rare occurrence but, it does happen, even after we have given the mirror the most stringent visual tests prior to coating. The dulling of the surface in these rare instances is usually very limited and detracts only from the mirror’s appearance, it has little or no effect on the mirror’s overall performance. The only way to remove this attack on the mirror’s surface if it is very noticeable and which may detract from it’s performance, is to re-polish and re-figure the mirror. This is usually very expensive and in some instances not possible.

We examine customer’s mirrors but, it is not possible to be 100% correct in all our assessments as to the finished, re-coated quality of a mirror’s surface.

NOTE: When we coat new mirrors and re-coats alike, the thickness of the aluminium layer and the enhancing layers of Hilux coatings are measured to within a few angstroms to give peak performance. The aluminium layer in particular is kept as thin as possible to avoid the slightest chance of producing a slight difference in thickness and possibly overall accuracy of the reflective surface. This process is checked regularly as described on our web site but we always err on the side of caution, If an optic is required to be centrally re-spotted there is a charge of £10 for this..

Keeping the thickness to a minimum has the effect of allowing a small fraction of a percent of light to pass through the aluminium, whilst still ensuring the overall efficiency of the coating lies in the 97% region of the visual and photographic spectrum. This very small and insignificant amount of light can be seen with the naked eye if a mirror is held up against a bright light, the very small amount of light is still sufficient to be able to see some bright objects through the coating. This is quite normal and it shows the coating process is working in it’s most efficient way possible by ensuring the reflective performance is above excellent and, there are no irregularities in the coating which could cause a problem. All prices shown are ex vat.