Iron oxide “Rouge”

it is'’ was one of the first polishing abrasive used by opticians , its properties make it still one of the best polishing agents ,but some contraindications have decreed the abandonment in favor of other products , fortunate in working iron oxide optical ended along with his fame at the start of production chemical industries of the early years 30.

ossido-di ferro


The chemical compounds formed from iron and oxygen are commonly called iron oxides.

The colour can vary from black to red to brown to yellow depending on the mineral constituent of which is iron oxide . Among the many species that has always interested opticians is the iron oxide ( ferric ) Red Fe2O3 and is a constituent of the mineral Hematite in addition to the main component of rust, where the typical red colour.

It is currently produced by industry as a pigment for paint and building materials, is easily available and costs an average of about 8 EUR per Kg. Looks like an impalpable touch red powder insoluble in water.

Normally iron oxide granules have average size around 1-2 microns, However being intended primarily to construction and paint factories, is not produced and distributed with controlled particle size and it is easy to find some dirt in the data sheets are indicated with a percentage varying from 0.5% to a 2 % sieve residue 0,045 mm. ("grit" 320 )


  • Surface quality: Definitely an excellent quality of polishing and shape accuracy produced.
  • Low cost: as stated above the retail price of iron oxide is not superior to 8 EUR per Kg


  • Grain size : the absence of a controlled particle size by producers prevents you from using the product without the filtering.
  • Slow action: the timing of polishing and corrections of the shape are significantly longer than other abrasives .
  • Colour fast: In the past the iron oxide was better known by the trade name “Lipstick lyrics English” or even “English Red” because of its ability to stain indelibly any fabric or material ( Apart from the glossy glass ) with whom he came into contact. This was a major cause of the abandonment of this product optical machining.


The first thing you need to do in order to shine with iron oxide is to filter the impurities through a settling process in water, as one larger grain would have devastating effects on the mirror surface filling it with numerous scratches.


proceedings: Take two glass jars from preserves and pour into a jar four or five tablespoons of oxide, then fill the jar to three-quarters of water and stir vigorously with a spoon for about fifteen seconds.

Wait a minute or two (*) that heavier grains resting on the bottom and then poured quickly, with a quick movement but not abrupt, half the content in the other jar.

Take the jar with half just paid ( the other can be disposed of , but absolutely don't pour it down the sink because once dried solidify blocking your pipes ) Wait for about 20 minutes or until all the filtered oxide has settled at the bottom, then pour gently the excess water to remain on the bottom of a fluid “Red slime”. This slime will be the mixture of abrasive used in polishing.


If despite the undoubted disadvantages we decide to do a test of working with iron oxide, It is good to keep in mind some aspects:

  • frictional heat: iron oxide granules have good resistance to fragmentation and maintain their sharp edges even after prolonged use. The heat produced by friction during the past greatly increases as speed increases of the same while the effectiveness and accuracy of processing decreases accordingly. it is'’ well then use past lens without being intimidated by the “hiss” product that seems to diminish in intensity with fast passes.
  • Another consequence of the heat produced is that the dried come relatively early, However within the first two or three dried, you do not need to change/add the mixture of nitric, which remains almost unchanged its abrasive properties for a long time, just add a little’ of water and start working again, you will see immediately regenerate a voluminous red foam, index of effective action of the product.


Were done two sessions complete with polishing-parabolizzazione upon a mirror from 125 mm f6 for polishing and a mirror 300 f 3.8 for parabolizzazione using the two different materials. Also using the same patina as well as tool and work techniques, We were able to highlight the differences in the results of processing attributable only to other abrasive.

The speed and ease of use combined with the good performance of surface quality and precision with cerium oxide justify the fact that it is the most widely used by manufacturers, surprisingly, the excellent surface quality and precision of form which can be reached with iron oxide, However the “price to pay” It is high in relation to time and ease of use, unlikely to ever stand up to his “colleague” in the preferences of grattavetro.

Here are the results of the comparison are summarized in this table

Good polishing/full time 15-30 hours 8-20 hours
Surface quality great good
Ability to resolve rows/scratches discrete good
Effective corrections good great
Amount for polishing ( mirror 125 mm ) 700 g 200 g
Grain size impure Pure/controlled
Time for fuel mixture 30 minutes immediate
Friction/smoothness good great
Miffed at 20 ° C short Media
Cleanliness scraps bad good
Availability widespread poor
Price Eur/Kg 8,00 90,00


There are more refined and specific products that are currently produced by industry that perform brilliantly on their task, described in This article, Although some important authors , argued that the use of iron oxide is preferable to the cerium oxide to surfaces where high accuracy is required, obtained in a pure form ( called “Rouge” ) using calcination iron oxalate (**) , While modern scientific and technological research is directing towards the production of nano-materials where the grain sizes are on the order of a few millionth of mm, However a “blast from the past” to retrace firsthand the roads of the Grand Masters grattavetri of past centuries can only be beneficial and instructive.

(*) the time for the filing of the granules can be used as a measure of their size , with two minutes of waiting we will have the certainty that only the smallest grains remain still in suspension, but the amount of filtered product will be really small, decreasing up to a minute this time will include it in the mixture even slightly larger granules, which will be still good for our purpose and will offer better quantity of mix can be used to the detriment of a minor, but still good ,refinement. Decreasing over the waiting time you begin to realize the possibility of finding ourselves too large granules that can only harm. As normally happens, the experience will tell what is the time that we have to wait to have the most effective measurement of granules.
(**) Jean Texereau – How to make a telescope – page. 40

3 comments on "iron oxide “Rouge””

  1. Giovanni

    I used the iron oxide, called “Lipstick” or even “nitric oxide from Jewelers”, but he never caused trouble to the surfaces. The real iron oxide for polishing the lenses is not the one used in construction, It is grainy, unclean, difficult to dissolve in water. But, but the one used in jewelry, It's very pure and top quality, mixes instantly, just shake a little the container (simple bottle of 0.5 l of mineral, with hole punctured with needle). The dilution, prepared for large areas, I added a little’ liquid soap, or detergent to facilitate the sliding of the glass above pitch. For a mirror from 200 mm it takes a few grams (two or three pair of soup spoons). The time to Polish a fund is long enough, in 20-30 actual hours and the surface is perfect. Other abrasives (cesium oxide and cerium) son faster but shine less well.
    One major problem is that lipstick stain and no longer goes away. And that red is also found on the clothes left in the closet, and often also on the sheets of the bed!! On hands, After a few days you still see halos and Red residues.
    I've owned about half a kilogram, After the earthquake I threw everything to the waste., together with the abrasive spoltiglia, at 800 and 1200. I was given a tribute by a manufacturer of lenses. What did I do wrong, I regretted it.

  2. Giovanni

    Sorry for the typo in the previous comment. Of lipstick from jewelers are needed 2-3 spoons, and not 2-3 pairs of spoons.

    • Massimo Marconi Massimo Marconi

      John, I agree, iron oxide polishing properties are superior to those of cerium oxide. The problem is not oxide used in construction in purity , but in grain size . The grain size analyses carried out by manufacturers indicate a residue on the sieve of 0,045 mm , on average by 2-4%.
      This is why you need a settling process in the water to be used, as a single larger oxide grain can do much damage on the shiny surface of the glass.
      The iron oxide can be obtained through different manufacturing processes, the one used in construction is taken from Hematite or other minerals containing iron oxide ( It is not found in nature in its pure State ), While that of jewelers, the “Rouge”, is obtained by calcination iron oxalate. Eventually the product obtained has the same iron oxide, just more refined.
      Building, Once the required particle size, It dilutes a great time, considering that the iron oxide is an insoluble material.
      Thanks anyway for your contribution, It is a pleasure to talk to another user of the “Lipstick” !

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