Does anybody know how this method works to reveal filed out numbers on aluminium crankcases? I know that it's got something to do with an acid which is applied to this area, and this acid reveals stresses in the aluminium. In that way the filed out numbers can be "seen" again.

Who's got more details about this method?

Cheers,
Jan

email (option): wd.register@gmail.com

Devon and Cornwall Constabulary.. ...Ian

email (option): ian@wright52.plus.com

Ian is right

Police forensics perform this on a regular basis

Some years ago we helped with this - but it was like witchcraft to us - we just provided sample test goods

I might still have a contact

Drop me a line jan

Job

email (option): Jonnyob1@googlemail.com

You may find this helpful
http://www.camaros.org/public/acidetch.txt
I bought an etching kit a while back, but it was missing it's leads, so I haven't bothered doing anything with it, it's up for grabs for what I paid for it (£20) , it has the etching fluids with it. I can't post it due to it's size and liquids etc, but if anyone wants it I'll hang onto it until someone can pick it up

email (option): davmax@ntlworld.com

Hi Jan

Many years ago I did a metallugry course as part of an engineering technician job. I didn't learn much about anything, but I vaguely remembering the acid etching tests for weld inspection.

That involved highly polishing the sample material and then etching with, I think, nitric acid. I remember hearing that this method could be used for recovering numbers on engine blocks.

The idea is that punching the numbers (with a number punch, of course) compresses the material under the number. The acid takes a little longer to eat away at that material, so if you "time" the test correctly and neutralise it with water at the right moment, the markings reveal themselves.

I don't think it's that complicated, and aluminium alloy deforms easier than, say, steel or cast iron. But I think it relies about meticulous polishing. And if the numbers aren't stamped hard enough, you won't have much to show for it.

Does that help?

email (option): dannydefazio@sumpmagazine.com

Thanks chaps! I also found an article here: http://www.intechopen.com/source/pdfs/13406/InTech-Metallographic_etching_of_aluminium_and_its_alloys_for_restoration_of_obliterated_marks_in_forensic_science_practice_and_investigations.pdf

It doesn't seem to be that easy: the acid mixture, the etching time, the preparation all seem to be quite important. And the acid that is used for cast iron doesn't seem to be the same as the acid for aluminium...

I think I'll ask our local police first... I've sponsored them a little while ago , so they should do something in return...

If anybody else has anything to add, go ahead!

Cheers,
Jan

email (option): wd.register@gmail.com

The acids are available from people who supply the etching kits, there are two acids one for ferrous and one for non ferrous, I don't think they are too expensive on their own

email (option): davmax@ntlworld.com

fireback x ray is another method and it doesnt involve acid, have a word with an archaeological science unit, they may be able to help, though primarilly of use for bringing out hidden detail within metal work it can also show up impressions and detail from stamping and its effect on the surrounding metal structure, its reasonably cheap, may be worth investigating,

seeing it stamped on aluminium would the blue dye used for finding cracks in alloy parts even try shining a bright light at different angles ie shining almost a flat angle and use different colours over the light

If this test became common practice there would certainly be a lot of red faces about..and mass suicide at the 'Gold Star' Owners Club.. ...Ian

email (option): ian@wright52.plus.com

hi,as john o b says x- raying has to be the way to go.
in industry its classed as non destructive testing.
polishing and acid etching may also remove more of whats left.
pipe fabrication people use the x-ray system to verify welds
are of the optimum quality.
perhaps a word in the right ear and a few pints may bring a result.
hope you get to the root of the number
cheers rick

email (option): richardholt@rocketmail.com

Thanks for the info chaps! Looks as if it won't be easy though...

Cheers,
Jan

email (option): wd.register@gmail.com

Hi jan

By chance yesterday at kempton I met a retired met police man I knew from his visits to our work place many years ago

He said to try acetone as it produces some half decent results ensuring you wash off after

He also mentioned that some of his colleagues used nail varnish remover in a crude way to try to obtain results - on the metal that is not on duty !!

As you have some ladies in the house they are bound to have such potions in stock, wash off after use

He also said results will be affected by the effect of the over stamping which also has a compressing effect under the surface

In such instances they had to use x ray facilities in pursuit of a result just as jon b indicated in an earlier post

Best regards

Jo'b

email (option): Jonnyob1@googlemail.com

Thanks for this info John! I can give this a try, it will do no harm !

Cheers,
Jan

email (option): wd.register@gmail.com

True an you may find out more about your inner self with the nail varnish remover

:-D

Jo'b

email (option): Jonnyob1@googlemail.com

Acid test:
1. Clean the casting, using a non-metallic tooth brush and a strong but completely volatile solvent such as acetone, MEK, lacquer thinner, toluene, Brake-Kleen, Gun Scrubber, etc.
2. Lay it flat on the bench, VIN upward.
3. Take good photos, this is the last time you'll ever see the stamp "as-is".
4. Make a little dam 1/2" high and 2" larger than the VIN all around it out of wax (does not dissolve in acid), like a line of candle drippings (some gasket makers may work, also). Don't get any fingerprints on the clean VIN surface.
5. Paint inside the dam with dilute hydrochloric acid.
6. Let it sit for 15 seconds or until you see bubbles.
7. Wash instantly with cold water, then again with baking soda several times to be sure it's completely neutralized.
8. Use a microscope if you have one, otherwise use a digital camera and zoom in.
9. Examine the image in Photoshop for a stain or a color change or a grainy line separating the VIN from the parent casting. Try playing with the color pallette to highlight changes.
10. If yes, the case was welded and a new boss either inserted or built up. Sometimes the inside of the casting also stains.
11. Alternative: the old VIN may show up as a shadow. If the boss was just ground down (no longer a favorite method) the original stamp strike distorts the metal to a depth about 2-1/2 times the stamp depth. If the VIN was .060" deep, the disturbance is .150" deep, and sometimes they don't grind deep enough and it will stain out.

email (option): sales@victorylibrary.com

Never seen a metallic toothbrush... ...Ian

email (option): ian@wright52.plus.com

Panic,

Thanks for the description! Will have to try this, but before I make an attempt on the actual engine, I'll do a few tests on a scrap engine. How much should the HCl be diluted?

Jan

email (option): wd.register@gmail.com

Most parts cleaner and welding brushes are stainless or brass.

Strong nerves: 50% acid.
Bad nerves: 10% acid.
Weaker will take much longer, but (duh) safer.
VERY important to neutralize afterward, when in doubt rinse again.

email (option): sales@victorylibrary.com

Thanks for the info!

Jan

email (option): wd.register@gmail.com

Good Luck, Jan ! If you're short of practice pieces, I've got several cases overstamped with workshop references that you're welcome to experiment on.

When you are diluting acid always remember 'acid in to water' NEVER 'water in to acid', or you will have exploding acid problems and we will all have to visit you in hospital. Gloves and goggles.

email (option): wariron@tpg.com.au

With modern ultrasound equipment you can pull up the numbers quite easily.
Otherwise a low dose X ray will also work very well.
I thought that wet methods went out of use 30 years ago.

It takes about 20 seconds to identify a variation in grain structure which confirms that the new numbers have been stamped onto a section welded in as the grains will be a different size and also in a different orientation.

If it confirms that there has been a weld done then go the next step and have an x ray determination done.
The new portable gear is amazing.
Safer, cleaner & totally non destructive.

Usually a trader college will do this all for free as it is excellent training for the NDT students and a lot more interesting than looking for defective welds.

Bike Beesa
trevor

email (option): wariron@tpg.com.au