diff --git a/overviewer_core/src/iterate.c b/overviewer_core/src/iterate.c
index 4cc853c..0fc1109 100644
--- a/overviewer_core/src/iterate.c
+++ b/overviewer_core/src/iterate.c
@@ -20,14 +20,21 @@
 static PyObject *textures = NULL;
 static PyObject *chunk_mod = NULL;
 static PyObject *blockmap = NULL;
+
+unsigned int max_blockid = 0;
+unsigned int max_data = 0;
+unsigned char *block_properties = NULL;
+
 static PyObject *known_blocks = NULL;
 static PyObject *transparent_blocks = NULL;
-static unsigned int max_blockid = 0;
-static unsigned int max_data = 0;
+static PyObject *solid_blocks = NULL;
+static PyObject *fluid_blocks = NULL;
+static PyObject *nospawn_blocks = NULL;
 
 PyObject *init_chunk_render(PyObject *self, PyObject *args) {
    
     PyObject *tmp = NULL;
+    unsigned int i;
     
     /* this function only needs to be called once, anything more should be
      * ignored */
@@ -50,12 +57,6 @@ PyObject *init_chunk_render(PyObject *self, PyObject *args) {
     blockmap = PyObject_GetAttrString(textures, "blockmap");
     if (!blockmap)
         return NULL;
-    known_blocks = PyObject_GetAttrString(textures, "known_blocks");
-    if (!known_blocks)
-        return NULL;
-    transparent_blocks = PyObject_GetAttrString(textures, "transparent_blocks");
-    if (!transparent_blocks)
-        return NULL;
     
     tmp = PyObject_GetAttrString(textures, "max_blockid");
     if (!tmp)
@@ -66,23 +67,44 @@ PyObject *init_chunk_render(PyObject *self, PyObject *args) {
         return NULL;
     max_data = PyInt_AsLong(tmp);
     
+    /* assemble the property table */
+    known_blocks = PyObject_GetAttrString(textures, "known_blocks");
+    if (!known_blocks)
+        return NULL;
+    transparent_blocks = PyObject_GetAttrString(textures, "transparent_blocks");
+    if (!transparent_blocks)
+        return NULL;
+    solid_blocks = PyObject_GetAttrString(textures, "solid_blocks");
+    if (!solid_blocks)
+        return NULL;
+    fluid_blocks = PyObject_GetAttrString(textures, "fluid_blocks");
+    if (!fluid_blocks)
+        return NULL;
+    nospawn_blocks = PyObject_GetAttrString(textures, "nospawn_blocks");
+    if (!nospawn_blocks)
+        return NULL;
+    
+    block_properties = calloc(max_blockid, sizeof(unsigned char));
+    for (i = 0; i < max_blockid; i++) {
+        PyObject *block = PyInt_FromLong(i);
+        
+        if (PySequence_Contains(known_blocks, block))
+            block_properties[i] |= 1 << KNOWN;
+        if (PySequence_Contains(transparent_blocks, block))
+            block_properties[i] |= 1 << TRANSPARENT;
+        if (PySequence_Contains(solid_blocks, block))
+            block_properties[i] |= 1 << SOLID;
+        if (PySequence_Contains(fluid_blocks, block))
+            block_properties[i] |= 1 << FLUID;
+        if (PySequence_Contains(nospawn_blocks, block))
+            block_properties[i] |= 1 << NOSPAWN;
+        
+        Py_DECREF(block);
+    }
+
     Py_RETURN_NONE;
 }
 
-int
-is_transparent(unsigned char b) {
-    PyObject *block = PyInt_FromLong(b);
-    int ret = PySequence_Contains(transparent_blocks, block);
-    if (!ret)
-    {
-        ret = !(PySequence_Contains(known_blocks, block));
-    }
-    Py_DECREF(block);
-    return ret;
-
-}
-
-
 unsigned char
     check_adjacent_blocks(RenderState *state, int x,int y,int z, unsigned char blockid) {
         /*
diff --git a/overviewer_core/src/overviewer.h b/overviewer_core/src/overviewer.h
index 934dae8..780b298 100644
--- a/overviewer_core/src/overviewer.h
+++ b/overviewer_core/src/overviewer.h
@@ -86,8 +86,32 @@ typedef struct {
     PyObject *right_blocks;
 } RenderState;
 PyObject *init_chunk_render(PyObject *self, PyObject *args);
-int is_transparent(unsigned char b);
 PyObject *chunk_render(PyObject *self, PyObject *args);
+typedef enum
+{
+    KNOWN,
+    TRANSPARENT,
+    SOLID,
+    FLUID,
+    NOSPAWN,
+} BlockProperty;
+/* globals set in init_chunk_render, here because they're used
+   in block_has_property */
+extern unsigned int max_blockid;
+extern unsigned int max_data;
+extern unsigned char *block_properties;
+static inline int
+block_has_property(unsigned char b, BlockProperty prop) {
+    if (b >= max_blockid || !(block_properties[b] & (1 << KNOWN))) {
+        /* block is unknown, return defaults */
+        if (prop == TRANSPARENT)
+            return 1;
+        return 0;
+    }
+    
+    return block_properties[b] & (1 << prop);
+}
+#define is_transparent(b) block_has_property((b), TRANSPARENT)
 
 /* pull in the rendermode info */
 #include "rendermodes.h"
diff --git a/overviewer_core/src/rendermode-overlay.c b/overviewer_core/src/rendermode-overlay.c
index 72e58ff..47c44fc 100644
--- a/overviewer_core/src/rendermode-overlay.c
+++ b/overviewer_core/src/rendermode-overlay.c
@@ -37,10 +37,6 @@ rendermode_overlay_start(void *data, RenderState *state, PyObject *options) {
     Py_DECREF(facemasks_py);
     
     self->white_color = PyObject_GetAttrString(state->chunk, "white_color");
-    
-    self->solid_blocks = PyObject_GetAttrString(state->textures, "solid_blocks");
-    self->fluid_blocks = PyObject_GetAttrString(state->textures, "fluid_blocks");
-    
     self->get_color = get_color;
     
     return 0;
@@ -52,8 +48,6 @@ rendermode_overlay_finish(void *data, RenderState *state) {
     
     Py_DECREF(self->facemask_top);
     Py_DECREF(self->white_color);
-    Py_DECREF(self->solid_blocks);
-    Py_DECREF(self->fluid_blocks);
 }
 
 static int
@@ -81,8 +75,7 @@ static void
 rendermode_overlay_draw(void *data, RenderState *state, PyObject *src, PyObject *mask, PyObject *mask_light) {
     RenderModeOverlay *self = (RenderModeOverlay *)data;
     unsigned char r, g, b, a;
-    PyObject *top_block_py, *block_py;
-    
+
     // exactly analogous to edge-line code for these special blocks
     int increment=0;
     if (state->block == 44)  // half-step
@@ -101,27 +94,19 @@ rendermode_overlay_draw(void *data, RenderState *state, PyObject *src, PyObject
         }
         
         /* check to be sure this block is solid/fluid */
-        top_block_py = PyInt_FromLong(top_block);
-        if (PySequence_Contains(self->solid_blocks, top_block_py) ||
-            PySequence_Contains(self->fluid_blocks, top_block_py)) {
+        if (block_has_property(top_block, SOLID) || block_has_property(top_block, FLUID)) {
             
             /* top block is fluid or solid, skip drawing */
-            Py_DECREF(top_block_py);
             return;
         }
-        Py_DECREF(top_block_py);
     }
     
     /* check to be sure this block is solid/fluid */
-    block_py = PyInt_FromLong(state->block);
-    if (!PySequence_Contains(self->solid_blocks, block_py) &&
-        !PySequence_Contains(self->fluid_blocks, block_py)) {
+    if (!block_has_property(state->block, SOLID) && !block_has_property(state->block, FLUID)) {
         
         /* not fluid or solid, skip drawing the overlay */
-        Py_DECREF(block_py);
         return;
     }
-    Py_DECREF(block_py);
 
     /* get our color info */
     self->get_color(data, state, &r, &g, &b, &a);
diff --git a/overviewer_core/src/rendermode-spawn.c b/overviewer_core/src/rendermode-spawn.c
index c303f23..275f33c 100644
--- a/overviewer_core/src/rendermode-spawn.c
+++ b/overviewer_core/src/rendermode-spawn.c
@@ -35,13 +35,10 @@ static void get_color(void *data, RenderState *state,
     /* default to no overlay, until told otherwise */
     *a = 0;
     
-    block_py = PyInt_FromLong(state->block);
-    if (PySequence_Contains(self->nospawn_blocks, block_py)) {
+    if (block_has_property(state->block, NOSPAWN)) {
         /* nothing can spawn on this */
-        Py_DECREF(block_py);
         return;
     }
-    Py_DECREF(block_py);
     
     blocklight = getArrayByte3D(self->blocklight, x, y, MIN(127, z_light));
     
@@ -72,7 +69,6 @@ rendermode_spawn_start(void *data, RenderState *state, PyObject *options) {
     
     /* now do custom initializations */
     self = (RenderModeSpawn *)data;
-    self->nospawn_blocks = PyObject_GetAttrString(state->textures, "nospawn_blocks");
     self->blocklight = PyObject_GetAttrString(state->self, "blocklight");
     self->skylight = PyObject_GetAttrString(state->self, "skylight");
     
@@ -87,7 +83,6 @@ rendermode_spawn_finish(void *data, RenderState *state) {
     /* first free all *our* stuff */
     RenderModeSpawn* self = (RenderModeSpawn *)data;
     
-    Py_DECREF(self->nospawn_blocks);
     Py_DECREF(self->blocklight);
     Py_DECREF(self->skylight);
     
diff --git a/overviewer_core/src/rendermodes.h b/overviewer_core/src/rendermodes.h
index 1a145cf..67bd598 100644
--- a/overviewer_core/src/rendermodes.h
+++ b/overviewer_core/src/rendermodes.h
@@ -143,8 +143,6 @@ extern RenderModeInterface rendermode_normal;
 typedef struct {
     /* top facemask and white color image, for drawing overlays */
     PyObject *facemask_top, *white_color;
-    /* only show overlay on top of solid or fluid blocks */
-    PyObject *solid_blocks, *fluid_blocks;
     /* can be overridden in derived classes to control
        overlay alpha and color
        last four vars are r, g, b, a out */
@@ -195,8 +193,6 @@ typedef struct {
     /* inherits from overlay */
     RenderModeOverlay parent;
     
-    /* used to figure out which blocks are spawnable */
-    PyObject *nospawn_blocks;
     PyObject *skylight, *blocklight;
 } RenderModeSpawn;
 extern RenderModeInterface rendermode_spawn;