"Rouge" Iron Oxide

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 , luck in the iron oxide optical processing is finished with his fame at the beginning of the industrial chemical production early 30.

FEATURES

The chemical compounds formed by ferro e oxygen They are commonly called iron oxides.

The color can vary from black to red to yellow to brown depending on the mineral constituent of which is iron oxide . Among the numerous existing species that has always been interested opticians is The iron oxide ( ferrico ) rosso Fe₂O₃ and is a constituent of the mineral hematite as well as the main component of the rust, from which the typical red coloration.

It is currently produced by the industry as a pigment for paints for building materials or, it is easy to find and costs an average of about 8 EUR per Kg. It appears as a red powder impalpable to the touch and insoluble in water.

Normally The iron oxide granules have an average size around 1-2 microns, However, it is intended primarily to the building and to colorifici, It is not produced and distributed with controlled particle size and is easy to find that the impurities in the technical sheets are indicated with a variable percentage by 0.5% to a 2 % residue through a sieve 0,045 mm. ("grit" 320 )

I PRO

• Surface quality: Surely an excellent polishing quality and accuracy of the resulting form.
• Low cost: as has been said the retail price of iron oxide is not higher than the 8 EUR per Kg

The VS

• Granulometry : the absence of a controlled particle size by manufacturers precludes the use of the product without a quote filtering.
• slow action: the timing of the polishing and the shape corrections are significantly longer compared to other abrasive .
• indelibly color: In the past the iron oxide was better known by the trade name “English lipstick” or also “English red” precisely because of its ability to indelibly stain any fabric or material ( apart from the polished glass ) with which he came into contact. This was a major cause of the abandonment of this product for optical processing.

PREPARATION FOR USE – SETTLING

The first operation to do in order to polish with the iron oxide is to filter the impurities present through a process of decantation in water, as a single granule size greater than it would have devastating effects on the mirror surface by filling it with numerous grooves.

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

Wait a minute or two (*) that heavier granules are resting on the bottom and then pour quickly, with a decisive but not abrupt movement, half of the contents in the other jar.

Take the jar with half just poured ( the other can be disposed of , but absolutely do not pour it down the sink because once dried solidify clogging the plumbing ) Wait twenty minutes or until all the oxide is filtered is deposited on the bottom, then gently pour the excess water until a fluid to remain on the bottom “red slime”. This will be the slime of abrasive mixture that we will use in polishing.

RECOMMENDATIONS FOR USE

If in spite of the undoubted disadvantages we decide to make a machining test with the iron oxide, it is good to keep some aspects in mind:

• frictional heat: the granules of 'iron oxide have a good resistance to fragmentation and retain their sharp edges even after prolonged use. The heat produced by friction during the past greatly increases with increasing speed of the same while the effectiveness and accuracy of machining decreases accordingly. Is’ well then use past lens undaunted by “hiss” product that appears to decrease in intensity with fast pass.
• Another consequence is that the heat produced The dried arrive relatively early, However, within the first two or three dried, it is not necessary to replace / add the mixture of oxide, which almost maintains its abrasive properties for a long time, just add a little’ water and return to work, You will be seen immediately regenerate a voluminous red foam, index of an effective action of the product.

OXIDE IRON OXIDE Vs CERIO, TEST COMPARATIVE GRATTAVETRO.

They were carried out two complete sessions polishing-parabolizzazione on a mirror 125 f6 mm for polishing and a mirror 300 F3.8 for parabolizzazione using the two different materials. Using also the same patina as well as tool and work techniques, They were able to highlight the differences in the processing results attributable only to the different abrasive.

The speed and simplicity of use combined with good quality performance and surface accuracy obtained with the cerium oxide justify the fact that it is the most widely used by manufacturers, surprisingly the excellent surface quality and accuracy of the shape which can be reached with the iron oxide, however the “price to pay” It is high in relation to time and ease of use, It is unlikely to ever take his head “fellow worker” in the grattavetro preferences.

Here are the results of the comparison summarized in this table

IN CONCLUSION

There are more refined and specific products that are being produced by the industry that successfully fulfill their duty, described this article, although some important authors , They argued that the use of the iron oxide is preferable for cerium oxide surfaces where a great accuracy is required, obtained in a pure form ( called “Rouge” ) through calcination of iron oxalate ^(**) , while the modern technological and scientific research is moving towards the production of nano-materials where the size of the granules are of the order of a few millionths of a millimeter, however a “blast from the past” to retrace firsthand the streets of the great masters of the past centuries grattavetri can only prove 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 smaller granules still remain in suspension, but the amount of filtered product will be very small, decreasing up to a minute this time we will include in the mixture also of slightly larger size granules, which will still good for our purpose and will offer a greater quantity of mixture used at the expense of a minor, but still good ,refinement. By decreasing over the wait time you start to realize the possibility of finding ourselves too large granules that can only do damage. As normally it happens experience will tell which is the time that we have to wait to have the measure of the most effective granules.

(**) Jean Texereau – How to make a telescope – page. 40