validation not working with file_column

I have installed the file_column plugin:
in my model i have this code:

validates_file_format_of :image, :in => ["gif", "png", "jpg"], :message
=> 'must be an image file'
  validates_filesize_of :image, :in => 0..800.kilobytes,
:too_large_message => 'mettine una + piccola'

  file_column :image,:magick=>{
      :geometry=>'600x600>',:attributes => { :quality => 60 },
      :versions => {
        :thumb => {:crop => "1:1", :geometry =>"30x30",:attributes => {
:quality => 50 } },
        :thumb_big=>{:crop => "1:1", :geometry =>"62x62",:attributes =>
{ :quality => 50 } }
      }
  }

validates_filesize_of not works.

Why?
How i can do?
Thanks