array (
  'post_type' => 'product',
  'post_status' => 'publish',
  'ignore_sticky_posts' => 1,
  'orderby' => 'title',
  'order' => 'DESC',
  'posts_per_page' => -1,
  'paged' => 0,
  'tax_query' => 
  array (
    'relation' => 'AND',
    0 => 
    array (
      'taxonomy' => 'pa_zwgrafoi',
      'terms' => 
      array (
        0 => 'Gravalos Panagiotis',
      ),
      'field' => 'name',
      'operator' => 'IN',
    ),
    1 => 
    array (
      'taxonomy' => 'pa_silloges',
      'terms' => 
      array (
        0 => 'Silkscreens',
      ),
      'field' => 'name',
      'operator' => 'IN',
    ),
  ),
)

array (
  'post_type' => 'product',
  'post_status' => 'publish',
  'ignore_sticky_posts' => 1,
  'orderby' => 'title',
  'order' => 'DESC',
  'posts_per_page' => -1,
  'paged' => 0,
  'tax_query' => 
  array (
    'relation' => 'AND',
    0 => 
    array (
      'taxonomy' => 'pa_zwgrafoi',
      'terms' => 
      array (
        0 => 'Gravalos Panagiotis',
      ),
      'field' => 'name',
      'operator' => 'IN',
    ),
    1 => 
    array (
      'taxonomy' => 'pa_silloges',
      'terms' => 
      array (
        0 => 'Painting',
      ),
      'field' => 'name',
      'operator' => 'IN',
    ),
  ),
)