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No doubt that sulfur, in the form of hydrogen sulfide, is the enemy of silver. The family silver needs a clean from time to time, but if it is just plated it needs to be done as rarely as possible. Sulfur is also the traditional enemy of art galleries in industrial cities. Old Masters used lead sulfate as their preferred white pigment, and over the years the surface of the paint would turn to lead sulfide, which is black, clearly the opposite of the artist’s intentions! The remedy here is to treat the surface with a solution of hydrogen peroxide which oxides sulfide back to sulfate, but that is not the answer with a delicate silver film. Best answer for a mirror is to keep it dry and airtight. For my aluminised mirrors I always used a piece of muslin stuffed with cotton wool which is placed right against the mirror surface. I don’t know what these modern anti tarnish papers contain, but I suppose that if you soaked a strip of paper with copper sulfate or lead acetate or lead nitrate solution and let it dry, the paper would absorb the gas in lieu of the mirror film. It should not be in contact with the mirror surface. You would then see the paper gradually take on a brownish or black tint with time, depending upon where you live. In fact chemists use lead acetate paper as a practical test for H2S gas. It goes black even with traces of the gas, long before the smell becomes apparent. I read that musicians sometimes use the anti tarnish paper in instrument cases. I don’t personally, but it would be effective for an instrument with silver plated keys, such as a flute. (Nickel plating is common, and does not involve the same problem.)
In conclusion, yes to the anti tarnish paper, yes to keeping the surface dry and as airtight as possible, and you can always try to make your own anti tarnish paper if you like! Just beware that lead and copper salts are poisonous.An excellent result. It shows that the method leaves a film that does not need burnishing, and that no special equipment is needed. Moreover the cost is not high, and Alan’s results after a few preliminary tests clearly demonstrates that expensive kits are not necessary to achieve success. What is necessary is great care in preparation of the surface and of the solutions. Well done!
By mistake I have posted the reply twice, and the second version is correct. I have now forgotten how to remove the first!
It sounds like the original coating was too thin. When you use a silvering solution, there are two types of silver deposited. One is a brown precipitate. This is silver, but not the desirable bright adherent silver film that coats the mirror. To avoid getting it on the mirror surface, the solution can be agitated, or the mirror silvered face down. A good deal of the silver ends up being wasted as the brown precipitate, which is the result of the silver ions getting reduced too quickly to form a continuous metallic coating. It cannot be avoided, as the reduction is done in solution.
The new silver film should be burnished, and it can be made more durable by applying a lacquer. One way to do this is to put the mirror on a record player turntable, rotate it slowly and apply the solution with a brush. Perspex chips can be dissolved in a solvent like ethyl acetate, though the solvent must not be one that evaporates too quickly, before the turntable has helped in spreading the solution.
Any trace of sulfur in the atmosphere will form a yellow-brown deposit of silver sulfide upon the surface, and it sounds like this happened in your case. It may be that in your location in Italy you have some sulfur dioxide or hydrogen sulfide in the atmosphere, in which case aluminising will be a better option. (Aluminium is less suited to observatories near the sea, unless it is overcoated. Chloride ions cause pitting corrosion of the film.) As an aside, I once aluminised a mirror myself. Chemically cleaned, placed upside down in a small vacuum chamber and suspended over a heating element upon which small turnings of aluminium had been hung….. Very interesting to do. The inside of the chamber gets coated as well, of course. 45 years later the mirror is still shiny!
I have seen videos of these kits in action and the results are impressive. The chemistry is nothing new, and I have used the materials over decades in my professional career when doing some chemical tests for reducing agents. The most important thing is to have the surface absolutely clean. If silvering a test tube or glass flask I would normally warm it with some concentrated nitric acid, but the acid can be added in the cold, as you would have to in the case of a mirror, or swabbed over the surface with cotton wool. The use of tin (II) chloride to sensitise the surface is also not a new invention, but is important in the spraying process for with that method the silver-based and reducer chemicals are in contact just briefly upon the surface of the mirror, and the pre-treatment with this powerful reducing agent will enhance the deposition rate of the silver. The price of the commercial kit is very high. Why not make your own? All the chemicals are readily obtained and silver nitrate can be bought for less than £2 per gram. You should not need more than 5 grams. There is a 12 page discussion on the Cloudy Nights Forum. Temperature is important. A warm day would work better, for in the lab one has to warm the reagents, and a large cold mirror surface will cool the spray. Again this is discussed at the Forum I mentioned. I would be inclined to have a go myself first at spraying a small test piece, rather than buying a kit. If you need any chemical advice I will be happy to help (by email).
I can’t help with this discussion on electronic searching, but I can add that we still have copies of the 1940-1990 journal index available (mentioned above by Bill Barton) if any member needs a copy. If there is no copy for sale at the online Shop, just contact me at the email address printed in the inside back cover of the latest Journal if you are interested.
The current volumes of the Journal have an annual index printed in the middle pages of the February issue of the following year. Before the early 1960s the index was always part of the last number of the same volume.
Well done to Bill for spotting this. There were BAA and RAS expeditions to Norway. The BAA one was summarised in a short Memoir at the time and in the large, rather rare hardback book which Martin gives the link to. The Memoir is one of those that was scanned for the CD edition of the BAA Memoirs which can be bought from our Shop. A pity that clouds prevailed, and that the only published photo shows the partially eclipsed Sun through cloud. The descriptions of the colours upon the clouds, and the landscape, are nice. The hardback book we do have in our collections, fortunately, and the pictures published in the album now for sale do look rather similar to those illustrated in it. The Archivists’ budget will not stretch to buying the item Bill has mentioned and, yes, doubtless it will become inaccessible in some private collection. The expedition was also marked by a set of 3×3 inch slides which covered similar subjects to the published hardback album. It was interesting to hear of the small print run of the hardback book. The books about the other 1890s BAA eclipse expeditions had a bigger print run, and are quite commonly to be found secondhand for a few tens of pounds each, and may even be currently available at that same book auction website. A company in India has been reprinting the latter books and other items, but I recommend that collectors try to obtain the original editions if possible, because the photographs will not likely have been reproduced at all well in the reprints. Of course, if anyone would like to buy the album Bill has drawn attention to and present it to the BAA, the archivists will be happy to hear from them!
There were two volumes of the Collected Works of Huggins published, and I was lucky to pick up the second in a Norfolk bookshop. Here is the frontispiece and a plate of his Jupiter drawings, for Huggins was also interested in planetary spectra. The book is one of the heaviest in my collection.
I recall this very point coming up at a lecture at last year’s Winchester weekend. Of course, it is well known that these camera images are enhanced. And some quite odd-looking colours can result from the combination of certain narrowband filters. Because news media are often uncritical, enhanced images can easily appear in print or on websites without any technical explanation of which filters have been combined. And members of the public think that the planet really looks like that. Sometimes the eyepiece view can help, and as I have been observing these planets since the 1970s I make a few comments.
The colours of Uranus and Neptune are similar when examined in the eyepiece. I have always described Uranus as slightly bluish-green, in reflectors of up to 1 metre aperture. That was again my experience several times late in 2023 using a 254 mm reflector. To my eye Neptune is just a little more bluish, but not much more so than Uranus. Of course, without a close conjunction, one cannot compare them in the same field of view!
I wonder if someone can work out when such an opportunity will occur? Doubtless it has already been done!
I think that Dominic has given an excellent and very clear explanation, and to add that as a speaker I am also sensitive to the fact that one’s slides might contain copyrighted images or other matter. And in any event, not all speakers give permission to have their talks recorded. I sometimes don’t permit it, perhaps for that reason, or perhaps because the talk was hastily prepared. When I look at the splendid PowerPoints put together by other people I always regret that I do not spend so much time preparing my folder of JPEGs which I simply show as a slideshow! We should be very grateful to Dominic and James and all those who have edited and uploaded video presentations.
…..And above all I just wanted to add my thanks to all those who organised and made this very enjoyable Winchester meeting possible.
If observers send me their location and accurate times I will be pleased to publish a summary of them in a later Section report in the Journal.
Richard McKim
I have received a number of images of the occultation and in a few cases the observer has selectively brightened Mars (for the reason stated above) and said so. This, provided it is stated, is no worse than if one did the same thing with a drawing. It seems to me that all the observers with whom I correspond do state clearly if they have modified an image. Because emails are not always kept, any modification should be stated UPON the image. The problem of surface brightness is of course more acute with Saturn when it is occulted by the Moon.
By the way, I am hoping I will receive all those nice images from all those who have posted on their member pages but did not formally send the image to the Mars (or Lunar!) Sections. Then your work will be acknowledged online and in any later report in print in the Journal.
Richard McKim
A view from Upper Benefield, Northants, under perfect conditions, with an 80 mm refractor. Some photos and timings close to the prediction for Birmingham. The observed times, plus or minus a second or two were 1st contact 04:58:25 and 2nd contact 04:58:56. Extremely cold with heavy frost. I hope others viewed this event. It was hard to see Mars with the naked eye close to the Moon.
Richard McKim
Thanks for providing these details Alex. The altitude for London is not too bad, even if the hour is not so convenient, and I hope that observers will send their successful results to the Mars Section in addition to posting them at their member pages. Some of our past Mars reports, all of which are available at the Section website, contain some nice images and drawings of past events. For example an occultation in 2003 was widely observed from the USA and there is a sequence of images by the late Don Parker. Good luck with the great British weather….!
Richard McKim
I am glad to see observers following this up. We did not have as many observations from the UK and Europe this time as I would have liked. But the western end of the storm, whose development we might have followed better, was decaying while the eastern part developed vigorously. The latter end was well observed on nearly every date from Japan, with some good observations on a few dates from Australia too. In America, observers could watch only the eastern limit of the dust as it appeared over Hellas (at the morning limb) in recent days. The storm closely followed the pattern of the large regional event of 2020 November, described in great detail in the Section blog for that year, with new cores forming in similar locations and ultimately a large dust cloud spilling over the boundaries of Hellas marking the eastern end. The pattern of fallout is however different at first glance, with the apparent boundaries of Argyre much enlarged. The small dust core imaged by John at Gallinaria Silva (just west of Solis Lacus) is the sort of phenomenon that continually renews this variable albedo feature.
Richard McKim
The dust storm continues as an impressive large regional event, and can now be observed at the terminator by sufficiently determined UK observers in the pre-dawn hours. If it continues for long enough, its western end will be even better placed in a few days’ time. I will be happy to receive and comment upon observations sent to me direct by email.
Richard McKim
Here is an update. I had an email this evening from Makoto Adachi just after 18.00UT, the local time in Japan being just after 2.00 a.m. He had just come indoors from the telescope to report upon the expansion of the storm. It has definitely expanded to the south, and Aurorae Sinus is now hidden by dust.
Richard McKim
