diff --git a/python/damask/_vtk.py b/python/damask/_vtk.py
index 2fd374f7c..7f3e64aef 100644
--- a/python/damask/_vtk.py
+++ b/python/damask/_vtk.py
@@ -40,20 +40,20 @@ class VTK:
         """
         Create VTK of type vtk.vtkRectilinearGrid.
 
-        This is the common type for results from the grid solver.
+        This is the common type for grid solver results.
 
         Parameters
         ----------
-        grid : numpy.ndarray of shape (3) of np.dtype = int
-            Number of cells.
-        size : numpy.ndarray of shape (3)
-            Physical length.
-        origin : numpy.ndarray of shape (3), optional
-            Spatial origin.
+        grid : iterable of int, len (3)
+            Number of cells along each dimension.
+        size : iterable of float, len (3)
+            Physical lengths along each dimension.
+        origin : iterable of float, len (3), optional
+            Spatial origin coordinates.
 
         """
         vtk_data = vtk.vtkRectilinearGrid()
-        vtk_data.SetDimensions(*(grid+1))
+        vtk_data.SetDimensions(*(np.array(grid)+1))
         coord = [np_to_vtk(np.linspace(origin[i],origin[i]+size[i],grid[i]+1),deep=True) for i in [0,1,2]]
         [coord[i].SetName(n) for i,n in enumerate(['x','y','z'])]
         vtk_data.SetXCoordinates(coord[0])
@@ -68,7 +68,7 @@ class VTK:
         """
         Create VTK of type vtk.vtkUnstructuredGrid.
 
-        This is the common type for results from FEM solvers.
+        This is the common type for FEM solver results.
 
         Parameters
         ----------
@@ -127,7 +127,7 @@ class VTK:
         fname : str or pathlib.Path
             Filename for reading. Valid extensions are .vtr, .vtu, .vtp, and .vtk.
         dataset_type : str, optional
-            Name of the vtk.vtkDataSet subclass when opening an .vtk file. Valid types are vtkRectilinearGrid,
+            Name of the vtk.vtkDataSet subclass when opening a .vtk file. Valid types are vtkRectilinearGrid,
             vtkUnstructuredGrid, and vtkPolyData.
 
         """
@@ -215,8 +215,8 @@ class VTK:
         Parameters
         ----------
         data : numpy.ndarray
-            Data to add. First dimension need to match either
-            number of cells or number of points
+            Data to add. First dimension needs to match either
+            number of cells or number of points.
         label : str
             Data label.
 
@@ -224,22 +224,21 @@ class VTK:
         N_points = self.vtk_data.GetNumberOfPoints()
         N_cells  = self.vtk_data.GetNumberOfCells()
 
-        if   isinstance(data,np.ndarray):
+        if isinstance(data,np.ndarray):
             if label is None:
                 raise ValueError('No label defined for numpy.ndarray')
 
-            if data.dtype in [np.float64, np.float128]:                                             # avoid large files
-                d = np_to_vtk(num_array=data.astype(np.float32).reshape(data.shape[0],-1),deep=True)
-            else:
-                d = np_to_vtk(num_array=data.reshape(data.shape[0],-1),deep=True)
+            N_data = data.shape[0]
+            d = np_to_vtk((data.astype(np.float32) if data.dtype in [np.float64, np.float128]
+                      else data).reshape(N_data,-1),deep=True)                               # avoid large files
             d.SetName(label)
 
-            if   data.shape[0] == N_cells:
+            if   N_data == N_cells:
                 self.vtk_data.GetCellData().AddArray(d)
-            elif data.shape[0] == N_points:
+            elif N_data == N_points:
                 self.vtk_data.GetPointData().AddArray(d)
             else:
-                raise ValueError(f'Invalid shape {data.shape[0]}')
+                raise ValueError(f'Cell / point count ({N_cells} / {N_points}) differs from data ({N_data}).')
         elif isinstance(data,pd.DataFrame):
             raise NotImplementedError('pd.DataFrame')
         elif isinstance(data,Table):
@@ -272,7 +271,7 @@ class VTK:
             if point_data.GetArrayName(a) == label:
                 return vtk_to_np(point_data.GetArray(a))
 
-        raise ValueError(f'array "{label}" not found')
+        raise ValueError(f'Array "{label}" not found.')
 
 
     def get_comments(self):