Mirror advice needed

[vr4]

I have a gso 12" dobsonian that i havent used for about 18months. When i got it out and went to set it up i noticed a discolouration around the edge of the primary mirror. I cant tell if its some sort of mould or if the surface of the mirror is starting to deteriorate as the scope is about 4 or 5 years old.

The rest of the mirror has only has minor dust but has anyone else experienced something like this? Im trying to decide if its worth the risk of trying to clean it off or if i should just leave it. I havent been able to see if it affects viewing quality due to the cloud cover over the last few days. The photo makes the rest of the mirror look a lot dirtier than it actually is but it shows the ring around the edge that im concerned about.

Any advice appreciated.
Thanks

[dannat]

just clean it with some soapy water, then try get a pic without the flash reflected in it -its hard to see the area exactly, [it looks to me like some of the mirror coating is coming off ]

[Wavytone]

Yes the coating is deteriorating. What causes it is moisture/humidity.

[vr4]

Thats what i was afraid of. Was thinking about selling it and getting a reasonable refractor as with my work hours its hard to get the time needed to use the dob with the long cooling times etc. Seems it's value has just dropped a lot.

[bigjoe]

Wouldn't be worth re coating either. Sell it as is.. and get a smaller dob or 5inch achro or Apo if you can afford one ..say at Bintel or TS ..if cool down is an issue.
bigjoe.

[GrahamL]

The coatings on all newts do need replacing in time , my old gso 12" mirror is in the cupboard available to anyone who wants it cheap but it needs recoating
.

Maybe you could mask off the edges and keep using it for a few more years
Its hard to tell how your mirror is fairing from that pic .. nothing good ever comes from photographing or staring at our mirrors , its always going to end in tears sooner or later, how much light is passing through it ? ,, look from the back .