RESEARCH POINT 1

The purpose of this research is, as I understand it, to look into methods  of paint application across a range of impressionists, post-impressionists, expressionists and 20th century pastel painters.
Impressionists
Monet was pre-occupied by capturing the fleeting effects of light and weather. Many painting give the impression flickering light. He was able to achieve this effect by using quick short brush strokes, slabs and dasher, small diagonal curving comma like marks and abrupt zig-zags. In La Gare St-Lazare there is a great sense of atmosphere and fleeting moment. Thick impasto and broken colour has been used. It is a restricted palette of muted complementary blues and oranges.
http://histoireontheway.blogspot.ie/2010_12_01_archive.html
Cezanne's style was as different as I think Pissaro and Monet's similar. It was typified by a distinctive look of solidity. Dense detailed modelling was used to build up a patchwork of smooth opaque shapes. His working method was slow and methodical. Even though he used thick paint, layering including wet-in-wet it is so light in place the canvas show through.
http://www.paul-cezanne.org/The-Card-Players-large.html
I see van Gogh's painting style as a kind of bridge between impressionism and expressionim.  He is famously known for his impastp brushwork often applied in swirling sinuous lines such as in the sky in Starry Night. At other times with short stabbing criss-cross and hatched strokes representing texture, and following contours. Early influence on him were the Dutch old masters and Dutch realist painters of that time. As a result of having spent some time with the impressionists he began painting outdoors. Many of the techniques acquired there weren't to last and he was soon experimenting with new technique using longer broader brushstrokes. When he moved to Arles he started to us brighter contrasting colours, reflecting the warm light of his surroundings. He was a great exponent on alla-prima, often working wet-in-wet. He began with un-diluted washes, also using a palette knife to draw attention to areas of more relief.
Wheatfield and Cypress Trees is a good example.
http://en.wikipedia.org/wiki/Wheat_Field_with_Cypresses#mediaviewer/File:Vincent_Willem_van_Gogh_049.jpg The calmness of the background of long blue swirling line contrasts with the short choppy strokes of the warm foreground.

Early 20th century German and Austrian Expressionism. Amongst its main proponents Wassily Kandinsky, Franz Marc, Ernst Ludwig Kirchner and Paula Modesohn-Becker. Many other artists have been described as Expressionists of one type or another since then.
This painting by Ernst Ludwig Kirchner is typical of the genre using saturated complementary colours and impasto paint
http://4.bp.blogspot.com/-XFcfa1nJbtc/ToYw8FyMGRI/AAAAAAAASAI/9zCokS0haVY/s1600/Ernst+Ludwig+Kirchner+-+Tutt%2527Art%2540+%25282%2529.jpg
Paula Modersohn-Becker's technique was quite diverse, ranging between soft and diffuse to distinctly hard edged with bright unrealistic colours. I think this self portrait  is a particularly good example the latter:
http://en.wikipedia.org/wiki/File:Paula_Modersohn-Becker_017.jpg

An impressive variety of her portraits are displayed on the following link:

http://bjws.blogspot.ie/2012/11/self-portraits-by-paula-modersohn.html
In  the self portrait - illustrated,  she has applied (as she so often did) distinct outlines, intense colours and slab like brush strokes - suggestive of Cezanne's style, who was an  influence on her own.

Self Portrait 1906, oil on paper

62.2 x 48.2 cm, 

Ludwig Roselius Museum, Bremen, Germany

A selection of 20th (and 21st) Century Pastel Painters:

Loosely applied spontaneous and inventive mark making - a beautiful cat painting in pastel pencil and colour wash by Elizabeth Blackadder:
http://www.pinterest.com/pin/244531454742611200/
The medium used is not described on the next one, but again looks very much like pastel had a big part to play. A wonderful webpage for viewing a wide array of cat paintings: http://www.ruthburts.com/2013_05_01_archive.html

Jason Bowyer uses soft or chalk pastels, inventively rubbing into both wet and dry ink to achieve stunning results:
http://www.russell-gallery.com/The-New-English-Art-Club-Group-Exhibition/images/010%20Jason%20Bowyer%2028x20.jpg  The contrast in marks between the pastel on wet ink and pastel on dry ink is quite evident.
Some food for thought in this short film of Jason Bowyer:
https://www.youtube.com/watch?v=FBlq1CLZZEc

Angela A'Court's still life paintings are minimalistic in nature. Line and form are emphasized and the compositions appear to be built up in many layers.
http://www.artistsinpastel.com/2012/12/angela-acourt.html
Taking a closer look it appears that more than one tone of each colour has been applied. It possible to view a selection of her work in great detail via this website:
https://artsy.net/artwork/angela-acourt-two-jugs-with-peony

Tony Allain describes himself as 'a brisk, no nonsense impressionist', aptly summing up my own response on looking at this example. In this landscape he appears to have employed the pastels on their sides, both horizontally and vertically giving a chunky hard edged look, and cleverly manages to make a complete statement with relatively few marks.
http://www.artistsinpastel.com/search/label/Tony%20Allain

Oversized cartoonish figures are the hallmark of Fernando Botero's work, containing an underlying serious political commentary. There appears to be a dense build up of layers giving a luminous quality to the surface, especially the woman's skin, in this painting:
http://museumsofohio.com/wp-content/uploads/2011/09/MoO_Woman.jpg
This blog describes the purpose of his work in some detail:
http://miryanb.blogspot.ie/2011/05/fernando-botero.html

Looking at Botero's figures called to mind Paula Rego's. There is no denying their powerful effect, again full of ambiguous narrative, they are altogether more disturbing to look at.
In a snapshot from a lengthy  interview on http://www.webofstories.com/play/paula.rego/42
she mentions beginning with hard pastels and finishing off with soft.
In Dog Woman 1994, pastel on canvas  a wide variety of mark making is evident. The skin looks to be made up of a mass of tonal blending and directional strokes, the shadows suggestive of knocks and bruises. Whereas the facial area has a broken crusty look.
http://culturoid.com/wp-content/uploads/2013/12/paula-rego-dog-woman.jpg

Odilon Redon's  pastels radiate a mysterious ephemeral atmosphere. He began to use this medium with oils later in his career, just before the turn of the 20th century. There is a velvety quality to the surface - perhaps aided by his use of wetted pastel, and wiping or brushing and applying fixative between layers. He also combined pastels with other media i.e. graphite for outlines, or black conte crayon.
http://www.wikiart.org/en/odilon-redon/lady-macbeth#supersized-artistPaintings-248047
Further artists of interest would be: Wolf Kahn and R.B. Kitaj.