var
  S: TBlobStream;
  B: pointer;
  c: integer;

...

  Table1.Edit;
  S := TBlobStream.Create(Table1BlobField as TBlobField, bmWrite); {кажется, так}
  C := S.write(B, C);
  Table1.Post;
  S.Destroy;

var
  S: TMemoryStream;
  B: pointer;
  C: integer;

...

S := TMemoryStream.Create;

...

  Table1.Edit;
  S.Clear;
  S.SetSize(C);
  C := S.write(B,C);
  (Table1BlobField as TBlobField).LoadFromStream(S);
  S.Clear;
  Table1.Post;

...

S.Destroy;