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Hardness Testing BS EN ISO 1518: BS 3900-E2 BS EN ISO 1522: BS 3900-E5 BS EN ISO 2815: BS 3900-E9 BS 3900-E17: ISO 12137- 1 BS 3900-E19: ISO 15184 ASTM D 3363

Scope and Field of Application

BS EN ISO 1518 and BS 3900-E2 are alternative names for the same method which is used to assess the resistance of a dry film of paint, varnish or related product to penetration by scratching with a needle.

BS EN ISO 1522 and BS 3900-E5 are alternative names for the same method which is used to assess the hardness of a dry film of paint, varnish or related product by measuring how it reduces the oscillation amplitude of a pendulum.

BS EN ISO 2815 and BS 3900-E9 are alternative names for the same method which is used to assess the resistance of a dry film of paint, varnish or related product to indentation by a weighted metal wheel.

BS 3900-E17 and ISO 12137-1 are alternative names for the same method which is used to assess the resistance of a dry film of paint, varnish or related product to marring by a looped or a ring-shaped stylus.

BS 3900-E19 and ISO 15184 are alternative names for the same method which is used to assess the hardness of organic coatings using a series of pencils with leads of known hardness.

ASTM D 3363 is a method which is similar to BS 3900-E19 : ISO 15184.

The temperature and humidity conditions of the test are specified in the standards.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

The actual standards are copyright-protected documents and we are not able to provide you with copies. If required however, you can easily obtain copies from either the British Standards Institution or the American Society for Testing and Materials.

Hardness has been defined as the ability of substances to abrade or indent one another and the original Mohr scale of hardness was based on a list of 10 minerals (ranging from talc to diamond) arranged in an order based on their ability to scratch one another. The methods described on this page all involve abrasion and/or indentation but in addition you may wish to refer to our abrasion and impact test pages.

 

Summary of Methods

BS EN ISO 1518: BS 3900-E2

The equipment used for this test consists of a horizontal motorised stage on which a coated panel is mounted. A weighted needle rests on the coated surface and forms part of an electric circuit which includes a meter. This meter deflects if the needle penetrates the coating and comes into contact with the metallic substrate.

During the test the coated panel is driven under the needle and the meter is observed in order to see if the coating is penetrated through to the substrate. After the test, any scratch formed on the coating is examined visually in order to assess the extent and nature of the damage.

The equipment can be used to determine the minimum load on the needle that will cause penetration through to the substrate. Alternatively it can be used to establish whether a specified needle loading will cause penetration.

 

BS EN ISO 1522: BS 3900-E5

There are two types of apparatus defined in this standard:-

• The Konig pendulum
• The Persoz pendulum

Both pendulums have spherical balls which rest on the coating under test and form the fulcrum. Both employ the same principle i.e. the softer the coating the more the pendulum oscillations are damped and the shorter the time needed for the amplitude of oscillation to be reduced by a specified amount. The two pendulums differ in shape, mass and oscillation time and there is no general relationship between the results obtained using the two pieces of equipment.

The test simply involves noting the time in seconds for the amplitude of swing to decrease form either 6 to 3 degrees (Konig pendulum) or 12 to 4 degrees (Persoz pendulum)

 

BS EN ISO 2815: BS 3900-E9

The apparatus used in this test is known as the Buchholz indenter. It consists of a sharp edged wheel (made of hardened tool steel) which is mounted in a rectangular block of metal fitted with two feet. When this apparatus rests on a horizontal surface, the effective load on the indenter is 500 grams.

The test involves placing the indenter on the coating and leaving it for 30 seconds. A x 20 magnification microscope fitted with an eyepiece graticule in then used, together with a light source, to measure the length in mm of the shadow cast by the indentation. The value obtained when 100 is divided by this length is known as the Buchholz Indentation Resistance of the coating.

 

BS 3900-E17: ISO 12137-1

The apparatus and the test method are virtually identical to those used in BS EN ISO 1518: BS 3900-E2. The main difference is in the nature of the stylus used. Whereas BS EN ISO 1518: BS 3900-E2 requires the use of a needle-shaped stylus, BS 3900-E17: ISO 12137-1 defines both a loop-shaped and a ring-shaped stylus, either of which can be used.

 

BS 3900-E19: ISO 15184

Artists' pencils are made with leads that range in hardness from 9H (very hard) to 9B (very soft). The test equipment consists of a set of 20 pencils together with a holder which allows a pencil to be held at a 45 degree angle while being pushed firmly across the surface of the coating under test. The use of the holder is optional.

The test procedure starts with the hardest pencil and continues using progressively softer pencils until the hardest pencil that does not mark the coating has been established. This is termed the "Pencil Hardness" of the coating. The standard defines "marking" of the coating as either:-

• a permanent indentation of the surface of the coating.
• a scratch or rupture of the surface of the coating.
• a combination of the above.

In addition the standard also allows for the determination of "Gouge Hardness" as defined in ASTM D 3363.

One limitation of this method is the lack of any international standard relating the hardness of pencil leads to any reference scale (e.g the Mohr scale of hardness).

It is our understanding that:-

• there are international variations in hardness. A Japanese HB pencil, for example, is softer than a European HB pencil which in turn is softer than a USA HB pencil.
• there is no standard method for measuring the hardness of pencils. Such methods that do exist rely on a skilled and experienced operative assessing the feel of the pencil when used as a drawing instrument and the blackness of the mark it produces.
• not all manufacturers produce pencils with consistent and reproducible hardness. Those that do usually have a retained set of pencils, dating back many years, with which current products are compared.
• the hardness of pencils can vary with time and is likely to be affected by the temperature at which they are stored.

BS 3900-E19: ISO 15184 lists manufacturers of pencils that have been found suitable for test use. In order to maximise the chances of different laboratories obtaining the same result when testing the same sample we would suggest that they use the same make and the same batch of pencils.

 

 

ASTM D 3363

This is a similar method to BS 3900-E19: ISO 15184. The main differences between the two methods are that ASTM D 3363:-

• only defines 14 pencils ranging in hardness from 6B to 6H.
• does not allow for the use of a pencil holder.
• defines "Scratch Hardness" as the hardest pencil that will not rupture or scratch the film ( this is essentially equivalent to "Pencil Hardness" as defined in BS 3900-E19: ISO 15184).
• defines "Gouge Hardness" as the hardest pencil that will not make a cut into the film which is at least 3 mm in length.

The same limitation regarding BS 3900-E19: ISO 15184 apply here also

 

Choice of Method

In some cases the test method will be specified but in others it is necessary to choose the most appropriate method. If you want a coating to be hard because it is going to be used on a floor subject to heavy traffic or on woodwork in a school room then you should consider if testing for resistance to abrasion or impact would be more appropriate.

In our opinion the advantages and limitations of the methods described on this page are as follows:-

 

Method	Advantages	Limitations
BS EN ISO 1518: BS 3900-E2	Capable of good reproducibility.	Needs flat test panel. Values obtained dependent on adhesion of coating to substrate. Equipment relatively expensive.
BS EN ISO 1522: BS 3900-E5	Capable of good reproducibility. Non-destructive. The best method of obtaining a value that depends on hardness alone.	Needs flat test panel. Hardness reported in units of time. Equipment relatively expensive.
BS EN ISO 2815: BS 3900-E9	Non-destructive. Simple and rapid to carry out. A good method of obtaining a value that depends on hardness alone.	Needs flat test panel. Hardness reported in units of reciprocal length. Many coatings are sufficiently plastic to render the indentation transient. It is often difficult to view the indentation especially in the case of dark-coloured coatings.
BS 3900-E17: ISO 12137-1	Capable of good reproducibility. Give a practical measure of the effect of hardness (i.e. resistance to marring). A good method for assessing the tendency of a coating to be scratched by finger nails car wash brushes etc.	Needs flat test panel. Values obtained dependent on adhesion of coating to substrate. Equipment relatively expensive.
BS 3900-E19: ISO 15184 ASTM D 3363	Simple and rapid to carry out. Hardness compared with that of familiar items. The only methods described on this page that can be carried out easily on site. Samples can be small and need not be flat if the pencil holder is not used.	The hardness of pencil leads is not well defined and not always well controlled Values obtained dependent on adhesion of coating to substrate. Results can be operator dependent especially when pencil holder not used. Judged by some to be trivial methods.

 

Sample Requirements

Our sample requirements are as follows:-

 

Method	Test Panel Size (mm)	Number of panels
BS EN ISO 1518: BS 3900-E2	125 x 100 x not greater than 1. Substrate must be metal. Coating must be non-conductive, smooth and more than 30 microns thick.	3
BS EN ISO 1522: BS 3900-E5	100 x 100 x 5. Substrate should be metal or glass and must be flat and rigid. Coating must be smooth and more than 30 microns thick.	2
BS EN ISO 2815: BS 3900-E9	150 x 100 x not less than 1. Substrate should be metal or glass and must be flat and rigid. The minimum coating thickness ranges from 15 microns for the hardest coatings to 35 microns for the softest.	2
BS 3900-E17: ISO 12137-1	125 x 100 x not greater than 1. The substrate and the coating thickness should be representative of the intended use of the coating.	3
BS 3900-E19: ISO 15184 (with pencil holder)	150 x 100 x any thickness and any material provided the substrate is flat and rigid. Coating must be smooth and more than 30 microns thick.	2
C (without pencil holder) ASTM D 3363	Can be as small as 10 x 10 on any smooth rigid substrate.	1

 

If you wish, we can prepare the test panels. The quantity of liquid paint we needs depends on the method of application. We will be pleased to advise you regarding our requirements.

 

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out all the tests listed on this page with the exception of BS 3900-E19: ISO 15184 and ASTM D 3363.

 

 

Please contact Peter Collins for further details.

 

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