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120" Realuminizing Project
22 February - 26 February, 2010

Photographs by Terry Pfister: 22 Feb 23 Feb 24 Feb 25 Feb 26 Feb
Photos by Dave Cowley


120" Aluminizing: Comments, Suggestions, Check-list items (to be folded into existing Procedures*)

Safety improvements

There is a need for safety improvements, and the preconditioning to have people not do things that could result in harm to humans and/or equipment. "Safety First."

  • Fall protection gear
  • Eye and fume protection
  • Railings around mirror handling cart
  • Finish railings for new steps to coating chamber control platform
  • Hard hats used more often in appropriate circumstances
  • Other safety gear:
    • Coveralls
    • Waterproof boots
    • Gloves
    • Hairnets

Pre-Planning (~1 month prior)

  • Assess need to aluminize before committing to the project. We should describe the reflectometry measurements in more detail. Historical measurements exist and the data should be collated and put in an Excel spreadsheet, which should help us determine the needed frequency of aluminizing.
  • Schedule five days for completion, if the night before the project begins is scheduled for observing. (Ideal situation is for the night before to be unscheduled.)
  • Assess safety precautions, i.e., railings, stairs, fall protection, etc.
  • Assess all safety gear: make sure there are sufficient hard hats, safety glasses, particle masks/respirators on hand.
  • Store up to three sets of tools specifically for this event so time is not lost looking for a ½-inch breaker or ½-to-3/8” converters, etc.


  • Donnie suggested that it might be helpful to have a quick  meeting each morning describing the tasks of the day.
  • Importance of initial telescope positioning, and the ability to move it a slight amount when it is unbalanced.
  • We can try to figure out a better park angle for the tub, but radial movers will be ideal.
  • In addition to the out-haul being too coarse, Bob mentions  that it should have a stronger support.
  • Specialty Supplies. Purchasing of ALL supplies for project should be codified as to who checks for supplies (both on campus and at the site), and who places the orders for needed supplies.
    • Vinyl roll for protecting metal parts from acid in stripping
    • Mylar for protecting clean mirror in transit
    • Insulating foil (until we switch to something else)
    • 2" Double-sided tape
    • 1" Double-sided tape
    • Black masking tape
    • Brown masking tape
    • Vinyl tape for dam (until we switch to something else)
    • Razor blades and holders
    • Aluminum staples for deposition
    • Soft natural sponges (PRE-SOFTENED)
    • Cloth towels for final cleaning (PRE-SOFTENED)
    • 2-Propanol for final cleaning


  • Threads on struts that lock the telescope were barely engaged. They are being modified so that they act like turn buckles and have a longer thread.
  • Need to have on hand: a power supply to rotate the tub, and air to release the brake.
  • Need special tools to loosen/tighten telescope fasteners (i.e., large ring wrenches).
  • Verify that pins for mirror cell have been located before beginning.
  • Review crane operator signals, and if appropriate, have radios for communication.
  • Need dedicated piano dollies with built-in clamps for large spreader bar.
  • Need pallet jack on site.
  • Need new, less flimsy flooring for the mirror cart.

Drew and others videoed the process.  It would be great to edit together official footage to show the whole process in order, and then have a viewing of the video the week beforehand, with all involved personnel, to refresh our memories of the process and problems.  There are a couple of videos on youtube.com of the 200" Palomar re-aluminizing process.  We should have something like this for in-house use.



Cleaning and Stripping

  • Jeff and Bill mentioned that we should change the way we insulate the mirror. Jeff had some ideas, and see Bill Brown's comment below.
  • Need four razor blade paint scrapers to use to clean the tape off the edge of the mirror.  The aged masking tape is hard to get off and needs to be scraped off.  Using hand held single-edged razor blades is hard on the fingers.  The process took four of us about an hour.  With the razor blade holders, the job would go a lot faster. http://www.labsafety.com/images/xl/STANLEY-Razor-Blade-Scraper-LSS-_i_LBD49579.jpg
  • Find a better dam material than masking tape doubled over on itself.  A roll of thick plastic or mylar about 3" wide could be taped around the edge of the mirror and stick up higher, which would keep the water spray more controlled and provide easier cleanup.  We had a hard time getting all the calcium carbonate cleaned away from the masking tape dam, and there was a lot of over spray of water because it was only 1/2" high. A taller fluid dam is preferable to the 1/4" high one.
  • Use vinyl tape as under-structure, rather than black masking tape, for easier clean-up.
  • Wear respirators when stripping the mirror with green river and washing with hydrochloric acid.  The best kind are the hooded ones, with air blown through filters.  It keeps the face mask from fogging and gives full visibility, plus it protects the eyes at the same time.
  • Need an inflator for the innertube.
  • Document each step in the mirror cleaning/stripping/final cleaning process with photos and detailed descriptions.
  • Stripping and Cleaning Supplies
       Cupric Sulphate
       De-Ionized water (made up there, I believe)
       Special cotton and cotton string to make giant swabs


  • The red tank needs servicing (pumps, valves, seals).
  • As far as repairs go, there was one set of aluminum staples that didn't fire (located at 5:30 position). Find out why they did not fire, and repair for next time.
  • Communication breakdown (due to roughing pump noise) was responsible for premature venting of the tank.
  • Hard to reach center of mirror in stripping operation; use a diving board instead of leaning on mirror. There are guardrails on the platform on either side of the mirror that a bridge could possibly be bolted to in order to allow access to the mirror center (maybe too risky to put in place but would sure be handy).
  • Place a 10-foot double-sided step ladder next to aluminizing tank.
  • Replace locking pins on the adjusters for the spreader bar back drive. Have spares on hand.
  • Need pan to put under cold trap for condensed water drips.
  • Locate spare diffusion pump, which may be crated up at the mountain.
  • Determine best way to purge tank after coating (Drew and Bill).
  • Check whether there is an operable heater and heater control on diffusion pump.
  • Install mirror to monitor oil level in both diffusion pumps.
  • Check whether there are spare diffusion pump coils. If so, have them on hand.


  • Pins for the mirror cell and radial movers for the tub.
  • New die(s) for the mirror support vertical counterweight threads.


The mirror should be “sampled” before washing, after washing, and after aluminizing. This should include a “Scotch tape test” to verify state of coating adhesion, reflectometry to determine its reflectance, and photographs to visually document mirror condition.


Bill Brown’s Observations:

  • Beryllium Contamination
    I have been in contact with Jim Schoonover about sampling pump oils for possible Be contamination. I need to follow through with Dan Blunk of EH&S for actual sampling techniques.
  •  Mirror Insulation
    Currently, no one seems to know the reason, scientific or otherwise, for insulating the mirror with cardboard and aluminum foil. I will contact Bob Thicksen, recently retired from Palomar Observatory, to get his insight on the matter. There are certainly better ways using more modern materials to do the insulating.
  • Mirror Cleaning and Stripping and Documentation process
    I have a good description of this for a document I prepared for NASA’s SOFIA project. Since it belongs to NASA, I would need to get approval to share the document. (I don’t think that there would be an issue with this).

Brian Dupraw’s suggestions:

There is a need to define responsibilities in providing supplies for the stripping and cleaning. We used several gallons of HCl, for instance. I think Bill made a special trip ahead of time to make sure the supplies were there. If they weren't, would he have ordered them himself or asked the mountain crew to order them? We brought up lots of our own supplies, which is fine... it would just be nice if it were codified so we don't one day discover we've forgotten something critical to the process, or assumed it would be waiting up there for us.


2006 Procedures assembled by Brian Dupraw

1993 Procedures

1993 Procedures with mark-up notes by Dave Cowley

1978 Procedures with Black and White Photos