Jump to content


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Mirror making: as raw materials as possible, as cheap as possible

  • Please log in to reply
3 replies to this topic

#1 Giorgos


    Ranger 4

  • -----
  • topic starter
  • Posts: 347
  • Joined: 14 Jan 2011
  • Loc: Athens, Greece

Posted 15 October 2019 - 12:24 AM

Hi all!

As the topic says I consider making a mirror on these principles


Glass: Plate glass 19mm thick (the thickest than can be found locally)

Tool: tile on plaster tool

Grinding abrasives:

Carborundum 80, 220, 400, 600

(the old books say that grinding can be finished with 600 so why  not? few abrasives for

economy and lower possibility of contamination, plate glass grinds really fast  especially with

carborundum which is very hard)

80 and 220 can be purchased very cheaply or even be given for free as they are used for sandblasting

by the ton, 400 and 600 can be purchased by gemstone polishing supplies stores.


Initial fast polishing with HCF (honeycomb foundation) lap, finishing with pitch (mixture of beeswax and pine rosin)

and rouge (very cheap from house construction supplies, has to be "washed" though by precipitation).

Foucault tester: no micrometers, no springs to take up slack only the old tried method by Rev. Ellison

of marking with a pencil the knife edge positions and reading the pencil marks with a fine scale and magnifying

glass. It can be made slitless though I guess.


The mirror will be 8" f/7-9, diagonal will be either purchased or cut rectangular from regular

window glass.

Any thoughts by experienced mirror makers?


Thank you in advance!

Edited by Giorgos, 15 October 2019 - 12:25 AM.

#2 macdonjh


    Fly Me to the Moon

  • *****
  • Posts: 5,785
  • Joined: 06 Mar 2006

Posted 15 October 2019 - 08:04 AM

I need to follow this... smile.gif


One of my bucket list items is to make a mirror.  I've purchased mirrors and built a scope, but never started from scratch.

#3 dan_h



  • *****
  • Posts: 2,937
  • Joined: 10 Dec 2007

Posted 15 October 2019 - 01:12 PM

Sixty years ago supplies could be difficult to obtain. That is not the case today. Economy of materials is not economy of effort.


Be wary of gemstone polishing supplies. They may not have sufficient purity of grit sizes. An single oversize grit on a gem lap does essentially no harm as it can be pushed harmlessly out of the way. Between two sheets of glass it can't escape before it causes grief.


If working by hand you will spend extra hours grinding and polishing with that sequence of grits. How much extra will depend on a number of things.  Not a real problem if machine grinding.  


IFF you have a good sphere with 80 grit you may be OK. If not so good a sphere, it will take a lot of effort with 220 to clean it up. A few ounces of 120 can save you a lot of time here.  Likewise at the end of fine grind. You can polish after 600 grit but you can save hours of hand polishing by finishing grinding with something finer than 600 or 25micron. A few ounces of 9-12 micron is a good thing.  Some folks will go as fine as 5 micron. 


Here is a link to a table of grit sizes. Use it to determine just how big you want to step between sizes.




The cost of aluminzing a mirror and any needed shipping to get it done is the same for an excellent piece of glass as it is for a very poor piece. I prefer to spend wisely here and ensure I am not wasting money on a mediocre piece. 


So in the end, it is your decision.  Sometimes what appears to be the easier way is not the best way.  






  • PrestonE and Augustus like this

#4 Oregon-raybender


    Optical Research Engineer

  • *****
  • Vendors
  • Posts: 799
  • Joined: 13 May 2010
  • Loc: Oregon, South Western Coast

Posted 16 October 2019 - 08:00 PM

If cheap you are asking money wise?. The listing you gave has a great deal of time, not money in finding,

working and processing the mirror. The cost is not in the materials but your efforts. Using my learned

skills of decades of work, I know what I can do make a mirror and scope with the resources about me.


You need to ask yourself what skills do have to follow this out. I suggest looking at what John Dobson 

has done, been there, done that. Find his book on making a mirror and scope.


Starry Nightswaytogo.gif

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Recent Topics

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics