Showing posts with label testing. Show all posts
Showing posts with label testing. Show all posts

Saturday, 22 December 2018

Lightfastness Testing #2 - Results 2018

Warning, Long post.  Maybe settle down with a cuppa and a biscuit while you read.
 
Well this isn't the post I thought I'd be writing when starting the Lightfast Testing earlier this year!
Because of the erratic weather in Wales, I thought that my Lightfast Tests would take longer than one summer.  I bought the Blue Wool Scale Cards to more easily know when the test paints had been given the right amount of light, 800 hours or more.  And thank goodness I did.


Some Operas perform better than others©Polly o'Leary 2018
Some Operas perform better than others



This summer was the hottest driest and sunniest in Wales since 1976 and because of this, the Lightfast Testing is now complete in just one summer ! I shouldn't be surprised really as the tests were hung outside for 126 hours roughly, though in the last few days they had to be brought in quickly when rain threatened.  Add to that the tests were hung outside for 8 to 10 hours a day throughout the summer and the 800 hours was exceeded.

About Lightfastmess Testing

First of all a note about Lightfastness Testing.  Most people realise that paints can fade over time, but did you know that paints can change in other ways?  Some can darken or become a different colour completely, though this happens less often.  Aureolin PY40, is one of those that change colour, becoming a dirty brown very quickly indeed.  Prussian Blue PB27, is another quirky pigment, I found it faded quickly but then recovered after being in the dark and didn't change after that!  Both Rose madder Genuine NR9 and Alizarin Crimson PR83, appeared not to change for a number of weeks, then very suddenly lost colour rapidly - most easily seen in the tints, which disappeared almost entirely, but fading was also evident in the mass tone too.

Aureolin Changed Completely! ©Polly o'Leary 2018
Aureolin Changed Completely!

Lightfastness Testing is conducted to give an indication of the maximum or minimum lifespan you can expect from a specific paint colour.  Some colours last just a few weeks, others last for a very long time - under favourable conditions, they can last for generations.

Most of the results agreed with the manufacturers' Lightfastness declarations, but there were a few surprises,  I leave the reader to work out which those were.

The Tests were measured against a Blue Wool Scale Textile Fading Card 1-8 which provided an estimate of the amount of light the paints had received, since our weather is so variable.  These cards can be bought from various companies in the UK including -

https://www.preservationequipment.com

http://www.conservation-resources.co.uk

https://www.sdcenterprises.co.uk

Prices as of November 2017 were around £16 per BWS 1-8 Card (the largest number of swatches) plus postage and packing.

If you live outside the UK, a google search of Blue Wool Scale Textile Fading Cards should bring up results relevant to your country.

Method

The tests were painted on Saunders Waterford Hot Press Watercolour Paper 200lb High White which has no optical brighteners.  They were then put into frames with thick, double layer aluminium strips taped to the inside of normal picture frame glass to cover half of each swatch, and a good contact ensured with the watercolour paper.  The frames were then hung outside in full sun at an angle of 45 degrees to ensure even exposure of all the paints over the whole test area.


Lightfastness Test Frames set at an angle of 45degrees©Polly o'Leary2018
Test Frames set at an angle of 45 degrees

The Blue Wool Scale 1-8 card was half covered with a double layer of thick aluminium foil and also framed tightly to ensure good contact between the aluminium and the unexposed wool swatches.  This was then also hung out daily at an angle of 45 degrees.  When not hung outside in the sunshine, the frames were laid face down on a table and covered to ensure no other light reached the paints or the Blue Wool Card, so that the results would be more reliable.

Main Test Page with results©Polly o'Leary 2018
Main Test Page with results

 Each week the tests were checked against the Blue Wool Cards, any changes noted, compared to the Blue Wool Scale and recorded against the paint.  The amount of change was also compared against the Blue wool Scale Card at the end of the test and recorded as a comparison.  The end of the test was the point at which the Blue wool Scale 8 swatch was noted as having changed.  Thanks to the glorious summer weather, this happened in a fraction of the time anticipated.

Blue Wool Scale Card 1-8 showing changes in colour©Polly o'Leary 2018
Blue Wool Scale Card 1-8 showing changes in colour

From my tests, it has become apparent that we have a wonderful selection of colours which are highly lightfast - Yellows, Reds, Pinks, Purples, Blues, Greens and Browns.  These can be found in the PDF - just follow the link.  If you have a problem seeing the PDF please contact me and let me know.
Polly o'Leary Lightfastness Testing Results 2018 PDF


A note about the paints/colours I tested

When choosing paints, it's important to remember that the only reliable guide as to the colour is the Pigment number.  Manufacturers may give different colours the same names, or the same colours different names, or they may change the pigments and leave the name the same, but the pigment number (or numbers if it's a mixture/hue) will let you know what you are really buying. 
These paints are my own paints, the fugitive colours have never been used in a painting, they may have been acquired as part of a set, or bought specifically for the test, especially where age could conceivably affect the lightfastness.  The rest are colours that are useful from time to time, apart from a core of colours which I find myself using in almost every painting.

The results of the tests are my results, under the conditions in my garden this summer (2018) and using the paints and paper that I normally use, against this brand of Blue Wool Scale 1-8 Card.  You may see different results with different paper and paint under different lighting conditions.  
These tests were conducted completely independent of any manufacturer or provider of art supplies.

More on Lightfastness and Colour

Lightfastness Testing #1.html 

How Many Colours Do You Need To Paint Flowers?  

The Problem Of PY153 - New Gamboge, Indian Yellow